Adaptive partition coding

ABSTRACT

Although wedgelet-based partitioning seems to represent a better tradeoff between side information rate on the one hand and achievable variety in partitioning possibilities on the other hand, compared to contour partitioning, the ability to alleviate the constraints of the partitioning to the extent that the partitions have to be wedgelet partitions, enables applying relatively uncomplex statistical analysis onto overlaid spatially sampled texture information in order to derive a good predictor for the bi-segmentation in a depth/disparity map. Thus, in accordance with a first aspect it is exactly the increase of the freedom which alleviates the signaling overhead provided that co-located texture information in form of a picture is present. Another aspect pertains the possibility to save side information rate involved with signaling a respective coding mode supporting irregular partitioning.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.15/663,256, filed Jul. 28, 2017, which is a Continuation of U.S.application Ser. No. 14/273,601 filed May 9, 2014, now U.S. Pat. No.9,756,330 which is a Continuation of International Application No.PCT/EP2012/072328, filed Nov. 9, 2012, and additionally claims priorityfrom U.S. Provisional Application No. 61/558,631, filed Nov. 11, 2011,all of which are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

The present invention is concerned with sample array coding usingcontour block partitioning or block partitioning allowing for a highdegree of freedom.

Many coding schemes compress sample array data using a subdivision ofthe sample array into blocks. The sample array may define a spatialsampling of texture, i.e. pictures, but of course other sample arraysmay be compressed using similar coding techniques, such as depth mapsand the like. Owing to the different nature of the information spatiallysampled by the respective sample array, different coding concepts arebest suited for the different kinds of sample arrays. Irrespective ofthe kind of sample array, however, many of these coding concepts useblock-subdivisioning in order to assign individual coding options to theblocks of the sample array, thereby finding a good tradeoff between sideinformation rate for coding the coding parameters assigned to theindividual blocks on the one hand and the residual coding rate forcoding the prediction residual due to misprediction of the respectiveblock, or finding a good comprise in rate/distortion sense, with orwithout residual coding.

Mostly, blocks are of rectangular or quadratic shape. Obviously, itwould be favorable to be able to adapt the shape of the coding units(blocks) to the content of the sample array to be coded. Unfortunately,however, adapting the shape of the blocks or coding units to the samplearray content involves spending additional side information forsignaling the block partitioning. Wedgelet-type partitioning of blockshas been found to be an appropriate compromise between the possibleblock partitioning shapes, and the involved side information overhead.Wedgelet-type partitioning leads to a partitioning of the blocks intowedgelet partitions for which, for example, specific coding parametersmay be used.

However, even the restriction to wedgelet partitioning leads to asignificant amount of additional overhead for signaling the partitioningof blocks, and accordingly it would be favorable to have a moreeffective coding concept at hand which enables a higher degree offreedom in partitioning blocks in sample array coding in a moreefficient way.

SUMMARY

According to an embodiment, a decoder for reconstructing a predeterminedblock of a depth/disparity map associated with a texture picture from adata stream may be configured to: segment a reference block of thetexture picture, co-located to the predetermined block, by thresholdingthe texture picture within the reference block to obtain abi-segmentation of the reference block into first and second partitions,spatially transfer the bi-segmentation of the reference block of thetexture picture onto the predetermined block of the depth/disparity mapso as to obtain first and second partitions of the predetermined block,and decode the predetermined block in units of the first and secondpartitions.

According to another embodiment, a decoder for reconstructing apredetermined block of a depth/disparity map associated with a texturepicture from a data stream may be configured to: segment a referenceblock of the texture picture, co-located to the predetermined block,depending on a texture feature of the texture picture within thereference block using edge detection or by thresholding the texturepicture, so as to obtain a bi-segmentation of the reference block intofirst and second partitions; spatially transfer the bi-segmentation ofthe reference block of the texture picture onto the predetermined blockof the depth/disparity map so as to obtain first and second partitionsof the predetermined block, and decode the predetermined block in unitsof the first and second partitions, wherein the decoder is configuredsuch that the segmentation, spatial transfer and decoding form one of afirst set of coding options of the decoder, which is not part of asecond set of coding options of the decoder, wherein the decoder isfurther configured to determine a dispersion of values of samples withinthe reference block of the texture picture; and retrieve a coding optionidentifier from the data stream, use the coding option identifier as anindex into the first set of coding options in case of the dispersionexceeding a predetermined threshold, with performing the segmentation,spatial transfer and decoding onto the predetermined block if the indexpoints to the one coding option, and as an index into the second set ofcoding options in case of the dispersion succeeding the predeterminedthreshold.

According to another embodiment, an encoder for encoding a predeterminedblock of a depth/disparity map associated with a texture picture into adata stream may be configured to: segment a reference block of thetexture picture, co-located to the predetermined block, by thresholdingthe texture picture within the reference block to obtain abi-segmentation of the reference block into first and second partitions,spatially transfer the bi-segmentation of the reference block of thetexture picture onto the predetermined block of the depth/disparity mapso as to obtain first and second partitions of the predetermined block,and encode the predetermined block in units of the first and secondpartitions.

According to still another embodiment, an encoder for encoding apredetermined block of a depth/disparity map associated with a texturepicture into a data stream may be configured to: segment a referenceblock of the texture picture, co-located to the predetermined block,depending on a texture feature of the texture picture within thereference block using edge detection or by thresholding the texturepicture so as to obtain a bi-segmentation of the reference block intofirst and second partitions; spatially transfer the bi-segmentation ofthe reference block of the texture picture onto the predetermined blockof the depth/disparity map so as to obtain first and second partitionsof the predetermined block, and encode the predetermined block in unitsof the first and second partitions, wherein the encoder is configuredsuch that the segmentation, spatial transfer and encoding form one of afirst set of coding options of the encoder, which is not part of asecond set of coding options of the encoder, wherein the encoder isfurther configured to determine a dispersion of values of samples withinthe reference block of the texture picture; and encode a coding optionidentifier into the data stream, use the coding option identifier as anindex into the first set of coding options in case of the dispersionexceeding a predetermined threshold, with performing the segmentation,spatial transfer and encoding onto the predetermined block if the indexpoints to the one coding option, and as an index into the second set ofcoding options in case of the dispersion succeeding the predeterminedthreshold.

According to another embodiment, a method for reconstructing apredetermined block of a depth/disparity map associated with a texturepicture from a data stream may have the steps of: segmenting a referenceblock of the texture picture, co-located to the predetermined block, bythresholding the texture picture within the reference block to obtain abi-segmentation of the reference block into first and second partitions,spatially transferring the bi-segmentation of the reference block of thetexture picture onto the predetermined block of the depth/disparity mapso as to obtain first and second partitions of the predetermined block,and decoding the predetermined block in units of the first and secondpartitions.

According to another embodiment, a method for reconstructing apredetermined block of a depth/disparity map associated with a texturepicture from a data stream may have the steps of: segmenting a referenceblock of the texture picture, co-located to the predetermined block,depending on a texture feature of the texture picture within thereference block using edge detection or by thresholding the texturepicture so as to obtain a bi-segmentation of the reference block intofirst and second partitions; spatially transferring the bi-segmentationof the reference block of the texture picture onto the predeterminedblock of the depth/disparity map so as to obtain first and secondpartitions of the predetermined block, and decoding the predeterminedblock in units of the first and second partitions, wherein the method isperformed such that the segmentation, spatial transfer and decoding formone of a first set of coding options, which is not part of a second setof coding options of the method, wherein the method further has thesteps of: determining a dispersion of values of samples within thereference block of the texture picture; and retrieving a coding optionidentifier from the data stream, using the coding option identifier asan index into the first set of coding options in case of the dispersionexceeding a predetermined threshold, with performing the segmentation,spatial transfer and decoding onto the predetermined block if the indexpoints to the one coding option, and as an index into the second set ofcoding options in case of the dispersion succeeding the predeterminedthreshold.

According to another embodiment, a method for encoding a predeterminedblock of a depth/disparity map associated with a texture picture into adata stream may have the steps of: segment a reference block of thetexture picture, co-located to the predetermined block, by thresholdingthe texture picture within the reference block to obtain abi-segmentation of the reference block into first and second partitions,spatially transfer the bi-segmentation of the reference block of thetexture picture onto the predetermined block of the depth/disparity mapso as to obtain first and second partitions of the predetermined block,and encode the predetermined block in units of the first and secondpartitions.

According to still another embodiment, a method for encoding apredetermined block of a depth/disparity map associated with a texturepicture into a data stream may have the steps of: segmenting a referenceblock of the texture picture, co-located to the predetermined block,depending on a texture feature of the texture picture within thereference block using edge detection or by thresholding the texturepicture so as to obtain a bi-segmentation of the reference block intofirst and second partitions; spatially transferring the bi-segmentationof the reference block of the texture picture onto the predeterminedblock of the depth/disparity map so as to obtain first and secondpartitions of the predetermined block, and encoding the predeterminedblock in units of the first and second partitions, wherein the method isperformed such that the segmentation, spatial transfer and encoding formone of a first set of coding options of the method, which is not part ofa second set of coding options of the method, wherein the method furtherhas the steps of: determining a dispersion of values of samples withinthe reference block of the texture picture; and encoding a coding optionidentifier into the data stream, using the coding option identifier asan index into the first set of coding options in case of the dispersionexceeding a predetermined threshold, with performing the segmentation,spatial transfer and encoding onto the predetermined block if the indexpoints to the one coding option, and as an index into the second set ofcoding options in case of the dispersion succeeding the predeterminedthreshold.

Another embodiment may have a computer program having a program code forperforming, when running on a computer, the above methods forreconstructing and encoding.

The main idea underlying the present invention is that althoughwedgelet-based partitioning seems to represent a better tradeoff betweenside information rate on the one hand and achievable variety inpartitioning possibilities on the other hand, compared to contourpartitioning, the ability to alleviate the constraints of thepartitioning to the extent that the partitions have to be wedgeletpartitions, enables applying relatively uncomplex statistical analysisonto overlaid spatially sampled texture information in order to derive agood predictor for the bi-segmentation in a depth/disparity map. Thus,in accordance with a first aspect it is exactly the increase of thefreedom which alleviates the signaling overhead provided that co-locatedtexture information in form of a picture is present.

Another thought on which a further aspect of the present invention isbased, is that the just-outlined idea according to which the derivationof a bi-segmentation based on a co-located reference block within apicture with subsequent transferal of the bi-segmentation onto thecurrent block of the depth/disparity map is merely reasonable if thelikelihood of achieving a good approximation of the content of thecurrent block of the depth/disparity map is sufficiently high so as tojustify the reservation of a respective predetermined value of acorresponding coding option identifier in order to trigger thisbi-segmentation transferal mode. In other words, side information ratemay be saved by avoiding the necessity to take the respectivepredetermined value of the coding option identifier for the currentblock of the depth/disparity map into account when entropy-coding thiscoding option identifier in case the respective bi-segmentationtransferal is very likely not to be selected anyway.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described in more detail belowwith respect to the figures, among which

FIG. 1 shows a block diagram of an multi-view encoder into whichembodiments of the present invention could be built in accordance withan example;

FIG. 2 shows a schematic diagram of a portion of a multi-view signal forillustration of information reuse across views and video depth/disparityboundaries;

FIG. 3 shows a block diagram of a decoder fitting to FIG. 1;

FIG. 4 shows a wedgelet partition of a quadratic block in continuous(left) and discrete signal space (right);

FIG. 5 shows a schematic illustration of the six different orientationsof Wedgelet block partitions;

FIG. 6 shows an Example of Wedgelet partition patterns for block size4×4 (left), 8×8 (middle), and 16×16 (right);

FIG. 7 shows an approximation of depth signal with Wedgelet model bycombining partition information and CPVs (mean value of depth signal inpartition regions);

FIG. 8 shows a generation of a Wedgelet partition pattern;

FIG. 9 shows a contour partition of a quadratic block in continuous(left) and discrete signal space (right);

FIG. 10 shows an example of Contour partition pattern for block size8×8;

FIG. 11 shows an approximation of depth signal with Contour model bycombining partition information and CPVs (mean value of depth signal inpartition regions);

FIG. 12 shows an intra prediction of Wedgelet partition (blue) for thescenarios that the above reference block is either of type Wedgeletpartition (left) or regular intra direction (right);

FIG. 13 shows a prediction of Wedgelet (blue) and Contour (green)partition information from texture luma reference;

FIG. 14 shows CPVs of block partitions: CPV prediction from adjacentsamples of neighboring blocks (left) and cross section of block (right),showing relation between different CPV types;

FIG. 15 shows a mode preselection based on texture luma variance;

FIG. 16 shows a block diagram of a decoder according to an embodiment;

FIG. 17 shows a block diagram of an encoder fitting to FIG. 16;

FIG. 18 shows a block diagram of a decoder according to an embodiment;

FIG. 19 shows a block diagram of an encoder fitting to FIG. 18;

FIG. 20 shows a block diagram of a decoder according to an embodiment;

FIG. 21 shows a block diagram of an encoder fitting to FIG. 20;

FIG. 22 shows a block diagram of a decoder according to an embodiment;

FIG. 23 shows a block diagram of an encoder fitting to FIG. 22;

FIG. 24 shows a block diagram of a decoder according to an embodiment;and

FIG. 25 shows a block diagram of an encoder fitting to FIG. 24.

DETAILED DESCRIPTION OF THE INVENTION

The following description of embodiments of the present invention startswith a possible environment into which embodiments of the presentinvention may be advantageously employed. In particular, a multi-viewcodec according to an embodiment is described with respect to FIGS. 1 to3. However, it should be emphasized that the embodiments describedthereinafter are not restricted to multi-view coding. Nevertheless, someaspects described further below may be better understood, and havespecial synergies, when used with multi-view coding, or, to be moreprecise, especially with the coding of depth maps. Accordingly, afterFIGS. 1 to 3, the description proceeds with an introduction intoirregular block partitioning and the problems involved therewith. Thisdescription refers to FIGS. 4 to 11 and forms a basis for thedescription of the embodiments of the present invention described afterthat.

As just said, the embodiments further outlined below use non-rectangularor irregular block partitioning and modeling functions in image andvideo coding applications and are particularly applicable to the codingof depth maps, such as for representing the geometry of a scene,although these embodiments would also be applicable to conventionalimage and video coding. The embodiments further outlined below furtherprovide a concept for using non-rectangular block partitioning andmodeling function in image and video coding applications. Theembodiments are particularly applicable to the coding of depth maps (forrepresenting the geometry of a scene), but are is also applicable toconventional image and video coding.

In multi-view video coding, two or more views of a video scene (whichare simultaneously captured by multiple cameras) are coded in a singlebitstream. The primary goal of multi-view video coding is to provide theend user with an advanced multimedia experience by offering a 3-dviewing impression. If two views are coded, the two reconstructed videosequences can be displayed on a conventional stereo display (withglasses). However, the necessitated usage of glasses for conventionalstereo displays is often annoying for the user. Enabling a high-qualitystereo viewing impression without glasses is currently an importanttopic in research and development. A promising technique for suchautostereoscopic displays is based on lenticular lens systems. Inprinciple, an array of cylindrical lenses is mounted on a conventionaldisplay in a way that multiple views of a video scene are displayed atthe same time. Each view is displayed in a small cone, so that each eyeof the user sees a different image; this effect creates the stereoimpression without special glasses. However, such autosteroscopicdisplays necessitate typically 10-30 views of the same video scene (evenmore views may be necessitated if the technology is improved further).More than 2 views can also be used for providing the user with thepossibility to interactively select the viewpoint for a video scene. Butthe coding of multiple views of a video scene drastically increases thenecessitated bit rate in comparison to conventional single-view (2-d)video. Typically, the necessitated bit rate increases approximatelylinearly way with the number of coded views. A concept for reducing theamount of transmitted data for autostereoscopic displays consists oftransmitting only a small number of views (perhaps 2-5 views), butadditionally transmitting so-called depth maps, which represent thedepth (distance of the real world object to the camera) of the imagesamples for one or more views. Given a small number of coded views withcorresponding depth maps, high-quality intermediate views (virtual viewsthat lie between the coded views)—and to some extend also additionalviews to one or both ends of the camera array-can be created at thereceiver side by a suitable rendering techniques.

In state-of-the-art image and video coding, the pictures or particularsets of sample arrays for the pictures are usually decomposed intoblocks, which are associated with particular coding parameters. Thepictures usually consist of multiple sample arrays (luminance andchrominance). In addition, a picture may also be associated withadditional auxiliary samples arrays, which may, for example, specifytransparency information or depth maps. Each picture or sample array isusually decomposed into blocks. The blocks (or the corresponding blocksof sample arrays) are predicted by either inter-picture prediction orintra-picture prediction. The blocks can have different sizes and can beeither quadratic or rectangular. The partitioning of a picture intoblocks can be either fixed by the syntax, or it can be (at least partly)signaled inside the bitstream. Often syntax elements are transmittedthat signal the subdivision for blocks of predefined sizes. Such syntaxelements may specify whether and how a block is subdivided into smallerblocks and being associated coding parameters, e.g. for the purpose ofprediction. For all samples of a block (or the corresponding blocks ofsample arrays) the decoding of the associated coding parameters isspecified in a certain way. In the example, all samples in a block arepredicted using the same set of prediction parameters, such as referenceindices (identifying a reference picture in the set of already codedpictures), motion parameters (specifying a measure for the movement of ablocks between a reference picture and the current picture), parametersfor specifying the interpolation filter, intra prediction modes, etc.The motion parameters can be represented by displacement vectors with ahorizontal and vertical component or by higher order motion parameterssuch as affine motion parameters consisting of six components. It isalso possible that more than one set of particular prediction parameters(such as reference indices and motion parameters) are associated with asingle block. In that case, for each set of these particular predictionparameters, a single intermediate prediction signal for the block (orthe corresponding blocks of sample arrays) is generated, and the finalprediction signal is built by a combination including superimposing theintermediate prediction signals. The corresponding weighting parametersand potentially also a constant offset (which is added to the weightedsum) can either be fixed for a picture, or a reference picture, or a setof reference pictures, or they can be included in the set of predictionparameters for the corresponding block. The difference between theoriginal blocks (or the corresponding blocks of sample arrays) and theirprediction signals, also referred to as the residual signal, is usuallytransformed and quantized. Often, a two-dimensional transform is appliedto the residual signal (or the corresponding sample arrays for theresidual block). For transform coding, the blocks (or the correspondingblocks of sample arrays), for which a particular set of predictionparameters has been used, can be further split before applying thetransform. The transform blocks can be equal to or smaller than theblocks that are used for prediction. It is also possible that atransform block includes more than one of the blocks that are used forprediction. Different transform blocks can have different sizes and thetransform blocks can represent quadratic or rectangular blocks. Aftertransform, the resulting transform coefficients are quantized andso-called transform coefficient levels are obtained. The transformcoefficient levels as well as the prediction parameters and, if present,the subdivision information is entropy coded.

Also state-of-the-art coding techniques such as ITU-T Rec. H.264|ISO/IECJTC 1 14496-10 or the current working model for HEVC are also applicableto depth maps, the coding tools have been particularly design for thecoding of natural video. Depth maps have different characteristics aspictures of a natural video sequence. For example, depth maps containless spatial detail. They are mainly characterized by sharp edges (whichrepresent object border) and large areas of nearly constant or slowlyvarying sample values (which represent object areas). The overall codingefficiency of multi-view video coding with depth maps can be improved ifthe depth maps are coded more efficiently by applying coding tools thatare particularly designed for exploiting the properties of depth maps.

In order to serve as a basis for a possible coding environment, in whichthe subsequently explained embodiments of the present invention may beadvantageously used, a possible multi-view coding concept is describedfurther below with regard to FIGS. 1 to 3.

FIG. 1 shows an encoder for encoding a multi-view signal in accordancewith an embodiment. The multi-view signal of FIG. 1 is illustrativelyindicated at 10 as comprising two views 12 ₁ and 12 ₂, although theembodiment of FIG. 1 would also be feasible with a higher number ofviews. Further, in accordance with the embodiment of FIG. 1, each view12 ₁ and 12 ₂ comprises a video 14 and depth/disparity map data 16,although many of the advantageous principles of the embodimentsdescribed further below could also be advantageous if used in connectionwith multi-view signals with views not comprising any depth/disparitymap data.

The video 14 of the respective views 12 ₁ and 12 ₂ represent aspatio-temporal sampling of a projection of a common scene alongdifferent projection/viewing directions. Advantageously, the temporalsampling rate of the videos 14 of the views 12 ₁ and 12 ₂ are equal toeach other although this constraint does not have to be necessarilyfulfilled. As shown in FIG. 1, advantageously each video 14 comprises asequence of frames with each frame being associated with a respectivetime stamp t, t−1, t−2, . . . . In FIG. 1 the video frames are indicatedby V_(view number, time stamp number). Each frame V_(1,t) represents aspatial sampling of the scene i along the respective view direction atthe respective time stamp t, and thus comprises one or more samplearrays such as, for example, one sample array for luma samples and twosample arrays with chroma samples, or merely luminance samples or samplearrays for other color components, such as color components of an RGBcolor space or the like. The spatial resolution of the one or moresample arrays may differ both within one video 14 and within videos 14of different views 12 ₁ and 12 ₂.

Similarly, the depth/disparity map data 16 represents a spatio-temporalsampling of the depth of the scene objects of the common scene, measuredalong the respective viewing direction of views 12 ₁ and 12 ₂. Thetemporal sampling rate of the depth/disparity map data 16 may be equalto the temporal sampling rate of the associated video of the same viewas depicted in FIG. 1, or may be different therefrom. In the case ofFIG. 1, each video frame v has associated therewith a respectivedepth/disparity map d of the depth/disparity map data 16 of therespective view 12 ₁ and 12 ₂. In other words, in the example of FIG. 1,each video frame V_(1,t) of view i and time stamp t has adepth/disparity map d_(1,t) associated therewith. With regard to thespatial resolution of the depth/disparity maps d, the same applies asdenoted above with respect to the video frames. That is, the spatialresolution may be different between the depth/disparity maps ofdifferent views.

In order to compress the multi-view signal 10 effectively, the encoderof FIG. 1 parallelly encodes the views 12 ₁ and 12 ₂ into a data stream18. However, coding parameters used for encoding the first view 12 ₁ arere-used in order to adopt same as, or predict, second coding parametersto be used in encoding the second view 12 ₂. By this measure, theencoder of FIG. 1 exploits the fact, according to which parallelencoding of views 12 ₁ and 12 results in the encoder determining thecoding parameters for these views similarly, so that redundanciesbetween these coding parameters may be exploited effectively in order toincrease the compression rate or rate/distortion ratio (with distortionmeasured, for example, as a mean distortion of both views and the ratemeasured as a coding rate of the whole data stream 18).

In particular, the encoder of FIG. 1 is generally indicated by referencesign 20 and comprises an input for receiving the multi-view signal 10and an output for outputting the data stream 18. As can be seen in FIG.2, the encoder 20 of FIG. 1 comprises two coding branches per view 12 ₁and 12 ₂, namely one for the video data and the other for thedepth/disparity map data. Accordingly, the encoder 20 comprises a codingbranch 22 _(v,1) for the video data of view 1, a coding branch 22 _(d,1)for the depth disparity map data of view 1, a coding branch 22 _(v,2)for the video data of the second view and a coding branch 22 _(d,2) forthe depth/disparity map data of the second view. Each of these codingbranches 22 is constructed similarly. In order to describe theconstruction and functionality of encoder 20, the following descriptionstarts with the construction and functionality of coding branch 22_(v,1). This functionality is common to all branches 22. Afterwards, theindividual characteristics of the branches 22 are discussed.

The coding branch 22 _(v,1) is for encoding the video 14 ₁ of the firstview 12 ₁ of the multi-view signal 12, and accordingly branch 22 _(v,1)has an input for receiving the video 14 ₁. Beyond this, branch 22 _(v,1)comprises, connected in series to each other in the order mentioned, asubtractor 24, a quantization/transform module 26, arequantization/inverse-transform module 28, an adder 30, a furtherprocessing module 32, a decoded picture buffer 34, two predictionmodules 36 and 38 which, in turn, are connected in parallel to eachother, and a combiner or selector 40 which is connected between theoutputs of the prediction modules 36 and 38 on the one hand theinverting input of subtractor 24 on the other hand. The output ofcombiner 40 is also connected to a further input of adder 30. Thenon-inverting input of subtractor 24 receives the video 14 ₁.

The elements 24 to 40 of coding branch 22 _(v,1) cooperate in order toencode video 14 ₁. The encoding encodes the video 14 ₁ in units ofcertain portions. For example, in encoding the video 14 ₁, the framesv_(1,k) are segmented into segments such as blocks or other samplegroups. The segmentation may be constant over time or may vary in time.Further, the segmentation may be known to encoder and decoder by defaultor may be signaled within the data stream 18. The segmentation may be aregular segmentation of the frames into blocks such as a non-overlappingarrangement of blocks in rows and columns, or may be a quad-tree basedsegmentation into blocks of varying size. A currently encoded segment ofvideo 14 ₁ entering at the non-inverting input of subtractor 24 iscalled a current block of video 14 ₁ in the following description ofFIGS. 1 to 3.

Prediction modules 36 and 38 are for predicting the current block and tothis end, prediction modules 36 and 38 have their inputs connected tothe decoded picture buffer 34. In effect, both prediction modules 36 and38 use previously reconstructed portions of video 14 ₁ residing in thedecoded picture buffer 34 in order to predict the current block enteringthe non-inverting input of subtractor 24. In this regard, predictionmodule 36 acts as an intra predictor spatially predicting the currentportion of video 14 ₁ from spatially neighboring, already reconstructedportions of the same frame of the video 14 ₁, whereas the predictionmodule 38 acts as an inter predictor temporally predicting the currentportion from previously reconstructed frames of the video 14 ₁. Bothmodules 36 and 38 perform their predictions in accordance with, ordescribed by, certain prediction parameters. To be more precise, thelatter parameters are determined be the encoder 20 in some optimizationframework for optimizing some optimization aim such as optimizing arate/distortion ratio under some, or without any, constraints such asmaximum bitrate.

For example, the intra prediction module 36 may determine spatialprediction parameters for the current portion such as an intraprediction direction along which content of neighboring, alreadyreconstructed portions of the same frame of video 14 ₁ isexpanded/copied into the current portion to predict the latter.

The inter prediction module 38 may use motion compensation so as topredict the current portion from previously reconstructed frames and theinter prediction parameters involved therewith may comprise a motionvector, a reference frame index, a motion prediction subdivisioninformation regarding the current portion, a hypothesis number or anycombination thereof.

The combiner 40 may combine one or more of predictions provided bymodules 36 and 38 or select merely one thereof. The combiner or selector40 forwards the resulting prediction of the current portion to theinserting input of subtractor 24 and the further input of adder 30,respectively.

At the output of subtractor 24, the residual of the prediction of thecurrent portion is output and quantization/transform module 36 isconfigured to transform this residual signal with quantizing thetransform coefficients. The transform may be any spectrally decomposingtransform such as a DCT. Due to the quantization, the processing resultof the quantization/transform module 26 is irreversible. That is, codingloss results. The output of module 26 is the residual signal 42 ₁ to betransmitted within the data stream. Not all blocks may be subject toresidual coding. Rather, some coding modes may suppress residual coding.

The residual signal 42 ₁ is dequantized and inverse transformed inmodule 28 so as to reconstruct the residual signal as far as possible,i.e. so as to correspond to the residual signal as output by subtractor24 despite the quantization noise. Adder 30 combines this reconstructedresidual signal with the prediction of the current portion by summation.Other combinations would also be feasible. For example, the subtractor24 could operate as a divider for measuring the residuum in ratios, andthe adder could be implemented as a multiplier to reconstruct thecurrent portion, in accordance with an alternative. The output of adder30, thus, represents a preliminary reconstruction of the currentportion. Further processing, however, in module 32 may optionally beused to enhance the reconstruction. Such further processing may, forexample, involve deblocking, adaptive filtering and the like. Allreconstructions available so far are buffered in the decoded picturebuffer 34. Thus, the decoded picture buffer 34 buffers previouslyreconstructed frames of video 14 ₁ and previously reconstructed portionsof the current frame which the current portion belongs to.

In order to enable the decoder to reconstruct the multi-view signal fromdata stream 18, quantization/transform module 26 forwards the residualsignal 42 ₁ to a multiplexer 44 of encoder 20. Concurrently, predictionmodule 36 forwards intra prediction parameters 46 ₁ to multiplexer 44,inter prediction module 38 forwards inter prediction parameters 48 ₁ tomultiplexer 44 and further processing module 32 forwardsfurther-processing parameters 50 ₁ to multiplexer 44 which, in turn,multiplexes or inserts all this information into data stream 18.

As became clear from the above discussion in accordance with theembodiment of FIG. 1, the encoding of video 14 ₁ by coding branch 22_(v,1) is self-contained in that the encoding is independent from thedepth/disparity map data 16 ₁ and the data of any of the other views 12₂. From a more general point of view, coding branch 22 _(v,1) may beregarded as encoding video 14 ₁ into the data stream 18 by determiningcoding parameters and, according to the first coding parameters,predicting a current portion of the video 14 ₁ from a previously encodedportion of the video 14 ₁, encoded into the data stream 18 by theencoder 20 prior to the encoding of the current portion, and determininga prediction error of the prediction of the current portion in order toobtain correction data, namely the above-mentioned residual signal 42 ₁.The coding parameters and the correction data are inserted into the datastream 18.

The just-mentioned coding parameters inserted into the data stream 18 bycoding branch 22 _(v,1) may involve one, a combination of, or all of thefollowing:

-   -   First, the coding parameters for video 14 ₁ may define/signal        the segmentation of the frames of video 14 ₁ as briefly        discussed before.    -   Further, the coding parameters may comprise coding mode        information indicating for each segment or current portion,        which coding mode is to be used to predict the respective        segment such as intra prediction, inter prediction, or a        combination thereof.    -   The coding parameters may also comprise the just-mentioned        prediction parameters such as intra prediction parameters for        portions/segments predicted by intra prediction, and inter        prediction parameters for inter predicted portions/segments.    -   The coding parameters may, however, additionally comprise        further-processing parameters 50 ₁ signaling to the decoding        side how to further process the already reconstructed portions        of video 14 ₁ before using same for predicting the current or        following portions of video 14 ₁. These further processing        parameters 50 ₁ may comprise indices indexing respective        filters, filter coefficients or the like.    -   The prediction parameters 46 ₁, 48 ₁ and the further processing        parameters 50 ₁ may even additionally comprise sub-segmentation        data in order to define a further sub-segmentation relative to        the aforementioned segmentation defining the granularity of the        mode selection, or defining a completely independent        segmentation such as for the appliance of different adaptive        filters for different portions of the frames within the        further-processing.    -   Coding parameters may also influence the determination of the        residual signal and thus, be part of the residual signal 42 ₁.        For example, spectral transform coefficient levels output by        quantization/transform module 26 may be regarded as correction        data, whereas the quantization step size may be signaled within        the data stream 18 as well, and the quantization step size        parameter may be regarded as a coding parameter.    -   The coding parameters may further define prediction parameters        defining a second-stage prediction of the prediction residual of        the first prediction stage discussed above. Intra/inter        prediction may be used in this regard.

In order to increase the coding efficiency, encoder 20 comprises acoding information exchange module 52 which receives all codingparameters and further information influencing, or being influenced by,the processing within modules 36, 38 and 32, for example, asillustratively indicated by vertically extending arrows pointing fromthe respective modules down to coding information exchange module 52.The coding information exchange module 52 is responsible for sharing thecoding parameters and optionally further coding information among thecoding branches 22 so that the branches may predict or adopt codingparameters from each other. In the embodiment of FIG. 1, an order isdefined among the data entities, namely video and depth/disparity mapdata, of the views 12 ₁ and 12 ₂ of multi-view signal 10 to this end. Inparticular, the video 14 ₁ of the first view 12 ₁ precedes thedepth/disparity map data 16 ₁ of the first view followed by the video 14₂ and then the depth/disparity map data 16 ₂ of the second view 12 ₂ andso forth. It should be noted here that this strict order among the dataentities of multi-view signal 10 does not need to be strictly appliedfor the encoding of the entire multi-view signal 10, but for the sake ofan easier discussion, it is assumed in the following that this order isconstant. The order among the data entities, naturally, also defines anorder among the branches 22 which are associated therewith.

As already denoted above, the further coding branches 22 such as codingbranch 22 _(d,1), 22 _(v,2) and 22 _(d,2) act similar to coding branch22 _(v,1) in order to encode the respective input 16 ₁, 14 ₂ and 16 ₂,respectively. However, due to the just-mentioned order among the videosand depth/disparity map data of views 12 ₁ and 12 ₂, respectively, andthe corresponding order defined among the coding branches 22, codingbranch 22 _(d,1) has, for example, additional freedom in predictingcoding parameters to be used for encoding current portions of thedepth/disparity map data 16 ₁ of the first view 12 ₁. This is because ofthe afore-mentioned order among video and depth/disparity map data ofthe different views: For example, each of these entities is allowed tobe encoded using reconstructed portions of itself as well as entitiesthereof preceding in the afore-mentioned order among these dataentities. Accordingly, in encoding the depth/disparity map data 16 ₁,the coding branch 22 _(d,1) is allowed to use information known frompreviously reconstructed portions of the corresponding video 14 ₁. Howbranch 22 _(d,1) exploits the reconstructed portions of the video 14 ₁in order to predict some property of the depth/disparity map data 16 ₁,which enables a better compression rate of the compression of thedepth/disparity map data 16 ₁, is theoretically unlimited. Coding branch22 _(d,1) is, for example, able to predict/adopt coding parametersinvolved in encoding video 14 ₁ as mentioned above, in order to obtaincoding parameters for encoding the depth/disparity map data 16 ₁. Incase of adoption, the signaling of any coding parameters regarding thedepth/disparity map data 16 ₁ within the data stream 18 may besuppressed. In case of prediction, merely the predictionresidual/correction data regarding these coding parameters may have tobe signaled within the data stream 18. Examples for suchprediction/adoption of coding parameters is described further below,too.

Remarkably, the coding branch 22 _(d,1) may have additional coding modesavailable to code blocks of depth/disparity map 16 ₁, in addition to themodes described above with respect to modules 36 and 38. Such additionalcoding modes are described further below and concern irregular blockpartitioning modes. In an alternative view, irregular partitioning asdescribed below may be seen as a continuation of the subdivision of thedepth/disparity map into blocks/partitions.

In any case, additional prediction capabilities are present for thesubsequent data entities, namely video 14 ₂ and the depth/disparity mapdata 16 ₂ of the second view 12 ₂. Regarding these coding branches, theinter prediction module thereof is able to not only perform temporalprediction, but also inter-view prediction. The corresponding interprediction parameters comprise similar information as compared totemporal prediction, namely per inter-view predicted segment, adisparity vector, a view index, a reference frame index and/or anindication of a number of hypotheses, i.e. the indication of a number ofinter predictions participating in forming the inter-view interprediction by way of summation, for example. Such interview predictionis available not only for branch 22 _(v,2) regarding the video 14 ₂, butalso for the inter prediction module 38 of branch 22 _(d,2) regardingthe depth/disparity map data 16 ₂. Naturally, these inter-viewprediction parameters also represent coding parameters which may serveas a basis for adoption/prediction for subsequent view data of apossible third view which is, however, not shown in FIG. 1.

Due to the above measures, the amount of data to be inserted into thedata stream 18 by multiplexer 44 is further lowered. In particular, theamount of coding parameters of coding branches 22 _(d,1), 22 _(v,2) and22 _(d,2) may be greatly reduced by adopting coding parameters ofpreceding coding branches or merely inserting prediction residualsrelative thereto into the data stream 28 via multiplexer 44. Due to theability to choose between temporal and inter-view prediction, the amountof residual data 42 ₃ and 42 ₄ of coding branches 22 _(v,2) and 22_(d,2) may be lowered, too. The reduction in the amount of residual dataover-compensates the additional coding effort in differentiatingtemporal and inter-view prediction modes.

In order to explain the principles of coding parameteradoption/prediction in more detail, reference is made to FIG. 2. FIG. 2shows an exemplary portion of the multi-view signal 10. FIG. 2illustrates video frame V_(1,t) as being segmented into segments orportions 60 a, 60 b and 60 c. For simplification reasons, only threeportions of frame V_(1,t) are shown, although the segmentation mayseamlessly and gaplessly divide the frame into segments/portions. Asmentioned before, the segmentation of video frame V_(1,t) may be fixedor vary in time, and the segmentation may be signaled within the datastream or not. FIG. 2 illustrates that portions 60 a and 60 b aretemporally predicted using motion vectors 62 a and 62 b from areconstructed version of any reference frame of video 14 ₁, which in thepresent case is exemplarily frame V_(1,t-1). As known in the art, thecoding order among the frames of video 14 ₁ may not coincide with thepresentation order among these frames, and accordingly the referenceframe may succeed the current frame V_(1,t) in presentation time order64. Portion 60 c is, for example, an intra predicted portion for whichintra prediction parameters are inserted into data stream 18.

In encoding the depth/disparity map d_(1,t) the coding branch 22 _(d,1)may exploit the above-mentioned possibilities in one or more of thebelow manners exemplified in the following with respect to FIG. 2.

-   -   For example, in encoding the depth/disparity map d_(1,t), coding        branch 22 _(d,1) may adopt the segmentation of video frame        V_(1,t) as used by coding branch 22 _(v,1). Accordingly, if        there are segmentation parameters within the coding parameters        for video frame V_(1,t), the retransmission thereof for        depth/disparity map data d_(1,t) may be avoided. Alternatively,        coding branch 22 _(d,1) may use the segmentation of video frame        V_(1,t) as a basis/prediction for the segmentation to be used        for depth/disparity map d_(1,t) with signaling the deviation of        the segmentation relative to video frame V_(1,t) via the data        stream 18. FIG. 2 illustrates the case that the coding branch 22        _(d,1) uses the segmentation of video frame V₁ as a        pre-segmentation of depth/disparity map d_(1,t). That is, coding        branch 241 adopts the pre-segmentation from the segmentation of        video V_(1,t) or predicts the pre-segmentation therefrom.    -   Further, coding branch 22 _(d,1) may adopt or predict the coding        modes of the portions 66 a, 66 b and 66 c of the depth/disparity        map d_(1,t) from the coding modes assigned to the respective        portion 60 a, 60 b and 60 c in video frame v_(1,t). In case of a        differing segmentation between video frame v_(1,t) and        depth/disparity map d_(1,t), the adoption/prediction of coding        modes from video frame v_(1,t) may be controlled such that the        adoption/prediction is obtained from co-located portions of the        segmentation of the video frame v_(1,t). An appropriate        definition of co-location could be as follows. The co-located        portion in video frame v_(1,t) for a current portion in        depth/disparity map d_(1,t), may, for example, be the one        comprising the co-located position at the upper left corner of        the current frame in the depth/disparity map d_(1,t). In case of        prediction of the coding modes, coding branch 22 _(d,1) may        signal the coding mode deviations of the portions 66 a to 66 c        of the depth/disparity map d_(1,t) relative to the coding modes        within video frame v_(1,t) explicitly signaled within the data        stream 18.    -   As far as the prediction parameters are concerned, the coding        branch 22 _(d,1) has the freedom to spatially adopt or predict        prediction parameters used to encode neighboring portions within        the same depth/disparity map d_(1,t) or to adopt/predict same        from prediction parameters used to encode co-located portions 60        a to 6 c of video frame v_(1,t). For example, FIG. 2 illustrates        that portion 66 a of depth/disparity map d_(1,t) is an inter        predicted portion, and the corresponding motion vector 68 a may        be adopted or predicted from the motion vector 62 a of the        co-located portion 60 a of video frame v_(1,t). In case of        prediction, merely the motion vector difference is to be        inserted into the data stream 18 as part of inter prediction        parameters 48 ₂.    -   In terms of coding efficiency, it might be favorable for the        coding branch 22 _(d,1) to have the ability to subdivide        segments of the pre-segmentation of the depth/disparity map        d_(1,t) using irregular block partitioning. Some irregular block        partitioning modes which the embodiments described further below        refer to, derive a partition information such as a wedgelet        separation line 70, from the reconstructed picture v_(1,t) of        the same view. By this measure, a block of the pre-segmentation        of the depth/disparity map d_(1,t) is subdivided. For example,        the block 66 c of depth/disparity map d_(1,t) is subdivided into        two wedgelet-shaped partitions 72 a and 72 b. Coding branch 22        _(d,1) may be configured to encode these sub-segments 72 a and        72 b separately. In the case of FIG. 2, both sub-segments 72 a        and 72 b are exemplarily shown to be inter predicted using        respective motion vectors 68 c and 68 d. According to sections 3        and 4, the coding branch 22 _(d,1) may have the freedom to        choose between several coding options for irregular block        partitioning, and to signal the choice to the decoder as side        information within the data stream 18.

In encoding the video 14 ₂, the coding branch 22 _(v,2) has, in additionto the coding mode options available for coding branch 22 _(v,1), theoption of inter-view prediction.

FIG. 2 illustrates, for example, that a portion 64 b of the segmentationof the video frame v_(2,t) is inter-view predicted from the temporallycorresponding video frame v_(1,t) of first view video 14 ₁ using adisparity vector 76.

Despite this difference, coding branch 22 _(v,2) may additionallyexploit all of the information available form the encoding of videoframe v_(1,t) and depth/disparity map d_(1,t) such as, in particular,the coding parameters used in these encodings. Accordingly, codingbranch 22 _(v,2) may adopt or predict the motion parameters includingmotion vector 78 for a temporally inter predicted portion 74 a of videoframe v_(2,t) from any or, or a combination of, the motion vectors 62 aand 68 a of co-located portions 60 a and 66 a of the temporally alignedvideo frame v_(1,t) and depth/disparity map d_(1,t), respectively. Ifever, a prediction residual may be signaled with respect to the interprediction parameters for portion 74 a. In this regard, it should berecalled that the motion vector 68 a may have already been subject toprediction/adoption from motion vector 62 a itself.

The other possibilities of adopting/predicting coding parameters forencoding video frame v_(2,t) as described above with respect to theencoding of depth/disparity map d_(1,t), are applicable to the encodingof the video frame V_(2,t) by coding branch 22 _(v,2) as well, with theavailable common data distributed by module 52 being, however, increasedbecause the coding parameters of both the video frame v_(1,t) and thecorresponding depth/disparity map d_(1,t) are available.

Then, coding branch 22 _(d,2) the depth/disparity map d_(2,t) similarlyto the encoding of the depth/disparity map d_(1,t) by coding branch 22_(d,1). This is true, for example, with respect to all of the codingparameter adoption/prediction occasions from the video frame v_(2,t) ofthe same view 12 ₂. Additionally, however, coding branch 22 _(d,2) hasthe opportunity to also adopt/predict coding parameters from codingparameters having been used for encoding the depth/disparity map d_(1,t)of the preceding view 12 ₁. Additionally, coding branch 22 _(d,2) mayuse inter-view prediction as explained with respect to the coding branch22 _(v,2).

After having described the encoder 20 of FIG. 1, it should be noted thatsame may be implemented in software, hardware or firmware, i.e.programmable hardware. Although the block diagram of FIG. 1 suggeststhat encoder 20 structurally comprises parallel coding branches, namelyone coding branch per video and depth/disparity data of the multi-viewsignal 10, this does not need to be the case. For example, softwareroutines, circuit portions or programmable logic portions configured toperform the tasks of elements 24 to 40, respectively, may besequentially used to fulfill the tasks for each of the coding branches.In parallel processing, the processes of the parallel coding branchesmay be performed on parallel processor cores or on parallel runningcircuitries.

FIG. 3 shows an example for a decoder capable of decoding data stream 18so as to reconstruct one or several view videos corresponding to thescene represented by the multi-view signal from the data stream 18. To alarge extent, the structure and functionality of the decoder of FIG. 3is similar to the encoder of FIG. 20 so that reference signs of FIG. 1have been re-used as far as possible to indicate that the functionalitydescription provided above with respect to FIG. 1 also applies to FIG.3.

The decoder of FIG. 3 is generally indicated with reference sign 100 andcomprises an input for the data stream 18 and an output for outputtingthe reconstruction of the aforementioned one or several views 102. Thedecoder 100 comprises a demultiplexer 104 and a pair of decodingbranches 106 for each of the data entities of the multi-view signal 10(FIG. 1) represented by the data stream 18 as well as a view extractor108 and a coding parameter exchanger 110. As it was the case with theencoder of FIG. 1, the decoding branches 106 comprise the same decodingelements in a same interconnection, which are, accordingly,representatively described with respect to the decoding branch 106_(v,1) responsible for the decoding of the video 14 ₁ of the first view12 ₁. In particular, each coding branch 106 comprises an input connectedto a respective output of the multiplexer 104 and an output connected toa respective input of view extractor 108 so as to output to viewextractor 108 the respective data entity of the multi-view signal 10,i.e. the video 14 ₁ in case of decoding branch 106 _(v,1). In between,each coding branch 106 comprises a dequantization/inverse-transformmodule 28, an adder 30, a further processing module 32 and a decodedpicture buffer 34 serially connected between the multiplexer 104 andview extractor 108. Adder 30, further-processing module 32 and decodedpicture buffer 34 form a loop along with a parallel connection ofprediction modules 36 and 38 followed by a combiner/selector 40 whichare, in the order mentioned, connected between decoded picture buffer 34and the further input of adder 30. As indicated by using the samereference numbers as in the case of FIG. 1, the structure andfunctionality of elements 28 to 40 of the decoding branches 106 aresimilar to the corresponding elements of the coding branches in FIG. 1in that the elements of the decoding branches 106 emulate the processingof the coding process by use of the information conveyed within the datastream 18. Naturally, the decoding branches 106 merely reverse thecoding procedure with respect to the coding parameters finally chosen bythe encoder 20, whereas the encoder 20 of FIG. 1 has to find an optimumset of coding parameters in some optimization sense such as codingparameters optimizing a rate/distortion cost function with, optionally,being subject to certain constraints such as maximum bit rate or thelike.

The demultiplexer 104 is for distributing the data stream 18 to thevarious decoding branches 106. For example, the demultiplexer 104provides the dequantization/inverse-transform module 28 with theresidual data 42 ₁, the further processing module 32 with thefurther-processing parameters 50 ₁, the intra prediction module 36 withthe intra prediction parameters 46 ₁ and the inter prediction module 38with the inter prediction modules 48 ₁. The coding parameter exchanger110 acts like the corresponding module 52 in FIG. 1 in order todistribute the common coding parameters and other common data among thevarious decoding branches 106.

The view extractor 108 receives the multi-view signal as reconstructedby the parallel decoding branches 106 and extracts therefrom one orseveral views 102 corresponding to the view angles or view directionsprescribed by externally provided intermediate view extraction controldata 112.

Due to the similar construction of the decoder 100 relative to thecorresponding portion of the encoder 20, its functionality up to theinterface to the view extractor 108 is easily explained analogously tothe above description.

In fact, decoding branches 106 _(v,1) and 106 _(d,1) act together toreconstruct the first view 12 ₁ of the multi-view signal 10 from thedata stream 18 by, according to first coding parameters contained in thedata stream 18 (such as scaling parameters within 42 ₁, the parameters46 ₁, 48 ₁, 50 ₁, and the corresponding non-adopted ones, and predictionresiduals, of the coding parameters of the second branch 16 _(d,1),namely 42 ₂, parameters 46 ₂, 48 ₂, 50 ₂), predicting a current portionof the first view 12 ₁ from a previously reconstructed portion of themulti-view signal 10, reconstructed from the data stream 18 prior to thereconstruction of the current portion of the first view 12 ₁ andcorrecting a prediction error of the prediction of the current portionof the first view 12 ₁ using first correction data, i.e. within 42 ₁ and42 ₂, also contained in the data stream 18. While decoding branch 106_(v,1) is responsible for decoding the video 14 ₁, a coding branch 106_(d,1) assumes responsibility for reconstructing the depth/disparity mapdata 16 ₁. See, for example, FIG. 2: The decoding branch 106 _(v,1)reconstructs the video 14 ₁ of the first view 12 ₁ from the data stream18 by, according to corresponding coding parameters read from the datastream 18, i.e. scaling parameters within 42 ₁, the parameters 46 ₁, 48₁, 50 ₁, predicting a current portion of the video 14 ₁ such as 60 a, 60b or 60 c from a previously reconstructed portion of the multi-viewsignal 10 and correcting a prediction error of this prediction usingcorresponding correction data obtained from the data stream 18, i.e.from transform coefficient levels within 42 ₁. For example, the decodingbranch 106 _(v, 1) processes the video 14 ₁ in units of thesegments/portions using the coding order among the video frames and, forcoding the segments within the frame, a coding order among the segmentsof these frames as the corresponding coding branch of the encoder did.Accordingly, all previously reconstructed portions of video 14 ₁ areavailable for prediction for a current portion. The coding parametersfor a current portion may include one or more of intra predictionparameters 50 ₁, inter prediction parameters 48 ₁, filter parameters forthe further-processing module 32 and so forth. The correction data forcorrecting the prediction error may be represented by the spectraltransform coefficient levels within residual data 42 ₁. Not all of theseof coding parameters need to transmitted in full. Some of them may havebeen spatially predicted from coding parameters of neighboring segmentsof video 14 ₁. Motion vectors for video 14 ₁, for example, may betransmitted within the bitstream as motion vector differences betweenmotion vectors of neighboring portions/segments of video 14 ₁

As far as the second decoding branch 106 _(d,1) is concerned, same hasaccess not only to the residual data 42 ₂ and the correspondingprediction and filter parameters as signaled within the data stream 18and distributed to the respective decoding branch 106 _(d,1) bydemultiplexer 104, i.e. the coding parameters not predicted by acrossinter-view boundaries, but also indirectly to the coding parameters andcorrection data provided via demultiplexer 104 to decoding branch 106_(v,1) or any information derivable therefrom, as distributed via codinginformation exchange module 110. Thus, the decoding branch 106 _(d,1)determines its coding parameters for reconstructing the depth/disparitymap data 16 ₁ from a portion of the coding parameters forwarded viademultiplexer 104 to the pair of decoding branches 106 _(v,1) and 106_(d,1) for the first view 12 ₁, which partially overlaps the portion ofthese coding parameters especially dedicated and forwarded to thedecoding branch 106 _(v,1). For example, decoding branch 106 _(d,1)determines motion vector 68 a from motion vector 62 a explicitlytransmitted within 48 ₁, for example, as a motion vector difference toanother neighboring portion of frame v_(1,t), on the on hand, and amotion vector difference explicitly transmitted within 48 ₂, on the onhand. Additionally, or alternatively, the decoding branch 106 _(d,1) mayuse reconstructed portions of the video 14 ₁ as described above withrespect to the prediction of the wedgelet separation line to derive anirregular block partitioning as briefly noted above with respect todecoding depth/disparity map data 16 ₁, and as will outlined in moredetail below.

To be even more precise, the decoding branch 106 _(d,1) reconstructs thedepth/disparity map data 14 ₁ of the first view 12 ₁ from the datastream by use of coding parameters which are at least partiallypredicted from the coding parameters used by the decoding branch 106_(v,1) (or adopted therefrom) and/or predicted from the reconstructedportions of video 14 ₁ in the decoded picture buffer 34 of the decodingbranch 106 _(v,1). Prediction residuals of the coding parameters may beobtained via demultiplexer 104 from the data stream 18. Other codingparameters for decoding branch 106 _(d,1) may be transmitted within datastream 108 in full or with respect to another basis, namely referring toa coding parameter having been used for coding any of the previouslyreconstructed portions of depth/disparity map data 16 ₁ itself. Based onthese coding parameters, the decoding branch 106 _(d,1) predicts acurrent portion of the depth/disparity map data 14 ₁ from a previouslyreconstructed portion of the depth/disparity map data 16 ₁,reconstructed from the data stream 18 by the decoding branch 106 _(d,1)prior to the reconstruction of the current portion of thedepth/disparity map data 16 ₁, and correcting a prediction error of theprediction of the current portion of the depth/disparity map data 16 ₁using the respective correction data 42 ₂.

The functionality of the pair of decoding branches 106 _(v,2) and 106_(d,2) for the second view 12 ₂ is, as already described above withrespect to encoding, similar as for the first view 12 ₁. Both branchescooperate to reconstruct the second view 12 ₂ of the multi-view signal10 from the data stream 18 by use of own coding parameters. Merely thatpart of these coding parameters needs to be transmitted and distributedvia demultiplexer 104 to any of these two decoding branches 106 _(v,2)and 106 _(d,2), which is not adopted/predicted across the view boundarybetween views 14 ₁ and 14 ₂, and, optionally, a residual of theinter-view predicted part. Current portions of the second view 12 ₂ arepredicted from previously reconstructed portions of the multi-viewsignal 10, reconstructed from the data stream 18 by any of the decodingbranches 106 prior to the reconstruction of the respective currentportions of the second view 12 ₂, and correcting the prediction erroraccordingly using the correction data, i.e. 42 ₃ and 42 ₄, forwarded bythe demultiplexer 104 to this pair of decoding branches 106 _(v,2) and106 _(d,2).

Decoding branch 106 _(d,2) may determine its coding parameters at lastpartially by adoption/prediction from coding parameters used by any ofdecoding branches 106 _(v,1), 106 _(d,1) and 106 _(v,2), from thereconstructed video 14 ₂ and/or from the reconstructed depth/disparitymap data 16 ₁ of the first view 12 ₁. For example, the data stream 18may signal for a current portion 80 b of the depth/disparity map data 16₂ as to whether, and as to which part of, the coding parameters for thiscurrent portion 80 b is to be adopted or predicted from a co-locatedportion of any of the video 14 ₁, depth/disparity map data 16 ₁ andvideo 14 ₂ or a proper subset thereof. The part of interest of thesecoding parameters may involve, for example, a motion vector such as 84,or a disparity vector such as disparity vector 82. Further, other codingparameters, such as regarding the irregularly partitioned blocks, may bederived by decoding branch 106 _(d,2).

In any case, the reconstructed portions of the multi-view data 10 arriveat the view extractor 108 where the views contained therein are thebasis for a view extraction of new views, i.e. the videos associatedwith these new views, for example. This view extraction may comprise orinvolve a re-projection of the videos 14 ₁ and 14 ₂ by using thedepth/disparity map data associated therewith. Frankly speaking, inre-projecting a video into another intermediate view, portions of thevideo corresponding to scene portions positioned nearer to the viewerare shifted along the disparity direction, i.e. the direction of theviewing direction difference vector, more than portions of the videocorresponding to scene portions located farther away from the viewerposition.

It should be mentioned that the decoder does not necessarily comprisethe view extractor 108. Rather, view extractor 108 may not be present.In this case, the decoder 100 is merely for reconstructing any of theviews 12 ₁ and 12 ₂, such as one, several or all of them. In case nodepth/disparity data is present for the individual views 12 ₁ and 12 ₂,a view extractor 108 may, nevertheless, perform an intermediate viewextraction by exploiting the disparity vectors relating correspondingportions of neighboring views to each other. Using these disparityvectors as supporting disparity vectors of a disparity vector fieldassociated with videos of neighboring views, the view extractor 108 maybuild an intermediate view video from such videos of neighboring views12 ₁ and 12 ₂ by applying this disparity vector field. Imagine, forexample, that video frame v_(2,t) had 50% of its portions/segmentsinter-view predicted. That is, for 50% of the portions/segments,disparity vectors would exist. For the remaining portions, disparityvectors could be determined by the view extractor 108 by way ofinterpolation/extrapolation in the spatial sense. Temporal interpolationusing disparity vectors for portions/segments of previouslyreconstructed frames of video 14 ₂ may also be used. Video frame v_(2,t)and/or reference video frame v_(1,t) may then be distorted according tothese disparity vectors in order to yield an intermediate view. To thisend, the disparity vectors are scaled in accordance with theintermediate view position of the intermediate view between viewpositions of the first view 12 ₁ and a second view 12 ₂. Detailsregarding this procedure are outlined in more detail below.

However, the embodiments outlined below may be advantageously used inthe framework of FIGS. 1 to 3 if considering merely the coding of oneview comprising a video and a corresponding depth/disparity map datasuch as the first view 12 ₁ of the above-outlined embodiments. In thatcase, the transmitted signal information, namely the single view 12 ₁,could be called a view synthesis compliant signal, i.e. a signal whichenables view synthesis. The accompanying of video 14 ₁ with adepth/disparity map data 16 ₁, enables view extractor 108 to performsome sort of view synthesis by re-projecting view 12 ₁ into aneighboring new view by exploiting the depth/disparity map data 16 ₁.Again, coding efficiency gain is obtained by using the irregular blockpartitioning. Thus, the irregular block partitioning embodimentsdescribed further below may be used within a single-view coding conceptindependent from the inter-view coding information exchange aspectdescribed above. To be more precise, the above embodiments of FIGS. 1 to3 could be varied to the extent that branches 22, 100 _(v/d,2) andassociated view 12 ₂ are missing.

Thus, FIGS. 1 to 3 showed an example for a multi-view coding conceptinto which the subsequently explained irregular block partitioning couldadvantageously be used. However, it is again emphasized that the codingmodes described below may also be used in connection with other sorts ofsample array coding, irrespective of the sample array being adepth/disparity map or not. Some of the coding modes described below donot even necessitate the coexistence of a depth/disparity map along witha corresponding texture map.

In particular, the embodiments outlined below involve some coding modes,by which the signal of a block is represented by a model that separatesthe samples of the signal into two sets of samples and represents eachset of samples by a constant sample value. Some of the below-explainedcoding modes can either be used for directly representing the signal ofa block or can be used for generating a prediction signal for the block,which is then further refined by coding additional residual information(e.g., transform coefficient levels). If one of the subsequentlyexplained coding modes is applied to depth signals, in addition to otherfavorable aspects, an advantage may result from the fact that the depthsignals are mainly characterized by slowing varying regions and sharpedges between slowly varying regions. While the slowly varying regionscan be efficiently represented by transform coding approaches (i.e.,based on a DCT), the representation of sharp edges between two nearlyconstant regions necessitate a large number of transform coefficients tobe coded. Such blocks containing edges can be better represented byusing a model that splits the block into two regions, each with aconstant sample value, as it is described with respect to some of thebelow-outlined embodiments.

In the following, different embodiments of the invention are describedin more detail. In sections 1 and 2, the basic concepts for partitioninga block into two regions of constant sample values are described.Section 3 describes different embodiments for specifying how a block canbe partitioned into different regions and what parameters need to betransmitted for representing the partitioning as well as the samplevalues for the regions. The embodiments include concepts for signalingthe partitioning information independent of any other block, forsignaling the partitioning information based on transmitted data forspatially neighboring blocks, and for signaling the partitioninginformation based on the already transmitted texture picture(conventional video picture) that is associated with the depth map to becoded. Thus, section 4 describes embodiments of the invention withrespect to the coding of mode information, partitioning information, andthe constant sample values involved with some embodiments for handlingan irregularly positioned block.

Although the following description is mainly targeted for the coding ofdepth maps (in particular in the context of multi-view video coding) andthe following description is based on given depth blocks, severalembodiments of the invention can also be applied for conventional videocoding. Hence, if the term “depth block” is replaced with the generalterm “signal block”, the description can be applied to other signaltypes. Furthermore, the following description sometimes concentrates onquadratic blocks, but the invention can also be applied to rectangularblocks or other connected or simply connected sets of samples.

1. Wedgelets

In block-based hybrid video coding, such as shown in FIGS. 1 to 3, forexample, a frame is subdivided in rectangular blocks. Often these blocksare quadratic and the processing for each block follows the samefunctional structure. Note that although most of the examples in thissection use quadratic blocks, Wedgelet block partitions and all relatedmethods are not limited to quadratic blocks, but are rather possible forany rectangular block size.

1.1. Wedgelet Block Partition

The basic principle of Wedgelet block partitions is to partition thearea of a block 200 into two regions 202 a, 202 b that are separated bya line 201, as illustrated in FIG. 4, where the two regions are labeledwith P₁ and P₂. The separation line is determined by a start point S andan end point E, both located on the block border. Sometimes, in thefollowing, region P₁ is called wedgelet partition 202 a, while region P₂is called wedgelet partition 202 b.

For the continuous signal space (see FIG. 4, left) the start pointposition is S(x_(S), y_(S)), and the end point position is E(x_(E),y_(E)), both limited to the block size 0≤x≤x_(E) and 0≤y≤y_(E) (whereone of the coordinates has to be equal to the minimum (0) or maximumvalue (x_(E) or y_(E))). According to these definitions the equation ofthe separation line is as follows:

$\begin{matrix}{y = {{{m \cdot x} + n} = {{\left( \frac{y_{E} - y_{S}}{x_{E} - x_{S}} \right) \cdot x} + \left( {y_{S} - {\frac{y_{E} - y_{S}}{x_{E} - x_{S}} \cdot x_{S}}} \right)}}} & (1)\end{matrix}$

Note that this equation is only valid for x₅≠x_(E). The two regions P₁and P₂ are then defined as the area left and right of the line,respectively.

In digital image processing usually a discrete signal space (see FIG. 4,right) is used, where the block consists of an integer number of samples203 illustrated by the grid squares. Here, the start and end points Sand E correspond to border samples of the block 200 with positionsS(u_(S), v_(S)), and E(u_(E), v_(E)), both limited to the block size0≤x≤u_(E) and 0≤y≤v_(E). In the discrete case the separation lineequation could be formulated according to (1). However, the definitionof the regions P₁ and P₂ is different here, as only complete samples canbe assigned as part of either of the two regions, illustrated in FIG. 4,right. This assignment problem may be solved algorithmically asdescribed in section 1.4.1.

Wedgelet block partitions 202 a, 202 b necessitate the start and endpoints 204 to be located on different edges of block 200. Consequently,six different orientations of Wedgelet block partitions 202 a, 202 b canbe distinguished for rectangular or quadratic blocks 200, as illustratedin FIG. 5.

1.2. Wedgelet Partition Patterns

For employing Wedgelet block partitions in the coding process, partitioninformation may be stored in the form of partition patterns. Such apattern consists of an array of size u_(E)×v_(E) and each elementcontains the binary information whether the according sample belongs toregion P₁ or P₂. FIG. 6 shows example Wedgelet partition patterns fordifferent block sizes. Here, the binary region information, i.e. thebi-segmentation, is represented by black or white samples 203.

1.3. Wedgelet Modeling and Approximation

For modeling the depth signal of a block with a Wedgelet, thenecessitated information conceptually consists of two elements. One isthe partition information (see section 1.1), e.g. in the form of apartition pattern, which assigns each sample 203 to one of the tworegions (see section 1.2). The other information element necessitated isthe values that are assigned to the samples of a region. The value ofeach of the two Wedgelet regions may be defined to be a constant. Thisis the case with some of the below-outlined embodiments. Thus, thisvalue will be referred as constant partition value (CPV). In that case,the second information element is composed of two representative samplevalues for the specified regions.

For approximating the signal of a depth block by a Wedgelet, the CPVs ofa given partition may be calculated as the mean value of the originaldepth signal of the corresponding region, as illustrated in FIG. 7. Atthe left hand side of FIG. 7 a grey-scaled portion out of arepresentative depth map is shown. A block 200 which is currently thesubject of wedgelet-based partitioning is exemplarily shown. Inparticular, its illustrative position within the original depth signal205 is shown, as well as an enlarged grey-scaled version. First, thepartition information, i.e. a possible bi-segmentation, in terms ofregions P₁ and P₂ is overlaid with the block 200. Then, the CPV of oneregion is calculated as the mean value of all samples covered by therespective region. As the partition information in the example in FIG. 5matches the depth signal 205 quite well, the resulting Wedglet model,i.e. the prediction of block 200 based on the wedgelet partitioning modeoutlined, with a lower CPV for region P₁ (darker grey) and a higher CPVfor region P₂ (brighter grey) represents a good approximation of thedepth block.

1.4. Wedgelet Processing 1.4.1 Wedgelet Pattern Lists

For the purpose of efficient processing and signaling of Wedgelet blockpartitions, partition patterns may be organized in lookup lists. Such aWedgelet pattern list contains the patterns for all possiblecombinations of start and end point positions for the region separationline or it contains a suitable subset of all possible combinations.Thus, one lookup list may be generated for each prediction block size.Identical lists may be made available at the encoder and the decoder, soas to enable the signaling between encoder and decoder (see section 3for details) relying on the position or index of a specific patternwithin the list of a certain block size. This can be implemented byeither including a pre-defined set of patterns or by executing theidentical generation algorithm as part of the encoder and decoderinitialization.

The core function for creating the Wedgelet partition pattern lookuplists is the generation of one list element, as illustrated in FIG. 8.This can be realized as described in the following (or by a similaralgorithm). Given an empty pattern (an u_(E)×v_(E) array of binaryelements) and the start point S and end point E coordinates (FIG. 8,left) the first step is to draw the separation line. For this purposethe Bresenham line algorithm can be applied. In general, the algorithmdetermines which samples 203 should be plotted in order to form a closeapproximation to a straight line between two given points. In the caseof Wedgelet partition patterns all elements 203 that approximate theline between start point S and end point E are marked (black boxes inFIG. 8, middle left). The last step is to fill one of the resulting tworegions separated by the marked samples. Here, the above mentionedassignment problem needs to be discussed. As the elements of a patternare binary, the separation line marked by the Bresenham algorithmbecomes part of one region. Intuitively this seems to be unbalanced, asline samples are theoretically part of both domains. However, it ispossible to assign the separation line samples to one region withoutloss of generality. This is assured by the fact that both the linemarking as well as the region filling algorithms are orientation aware,i.e. relative to the root corner of the according orientation. Based onthe fact, that the corner region is completely delimited by theseparation line, filling this region is relatively simple. The fillingalgorithm starts with a root corner element 206 and consecutively marksall pattern elements column- and line-wise until it reaches an elementthat is already marked and thus part of the line 207 (see FIG. 8, middleright). As a result, the Wedgelet partition pattern for the given startand end point position is represented by the binary values (FIG. 8,right).

The generation process for the Wedgelet partition pattern lookup listsof a certain block size consecutively creates list elements for possibleline start and end positions. This is realized by iterating over the sixorientations shown in FIG. 5. For each orientation, the start positionsare located on one and the end positions on another edge of the blockand the list generation process executes the Wedgelet pattern generationmethod introduced above for each possible combination of start and endpositions. For efficient processing and signaling, the Wedgelet patternlists should only contain unique patterns. Therefore, before a newpattern is added to the list, it is checked for being identical orinverse identical to any of the patterns already in the list. In such acase, the pattern is redundant and therefore discarded. In addition tothat, plane patterns, i.e. all samples are assigned to one region, arealso excluded from the list as they are not representing a validWedgelet block partition.

As an extension to the described Wedgelet pattern lists, the resolutionof line start and end positions used for generating the patterns can beadaptively increased or decreased, e.g. depending on the block size. Thepurpose of this extension is to find a better trade-off between codingefficiency and complexity. Increasing the resolution leads to a listwith more patterns, while decreasing the resolution results in a shorterlist, compared to normal resolution. Consequently, the resolution istypically increased for small block sizes and decreased for large blocksizes. It is important to note that independent of the resolution forstart and end positions, the Wedgelet partition patterns stored in thelist is necessitated to have normal resolution, i.e. the original blocksize. Decreasing the resolution can be simply realized by generating thepatterns as described above, but only for a subset of start and endpositions. For example half the resolution means to limit the patterngeneration to every second start and end position. In contrast to that,increasing the resolution is more difficult. For covering all start andend positions a temporary pattern with the increased resolution isgenerated first, using the algorithm described above. In a second stepthe resulting pattern is down-sampled to regular resolution. Note thatfor binary data, down-sampling does not support interpolated values,which results in a larger number of identical patterns for the case ofan increased resolution.

As the final result of the Wedgelet pattern generation described above,an ordered list of Wedgelet patterns is derived at both encoder anddecoder side. In an actual implementation, these patterns can also bepredefined by the employed coding algorithm/coding standard.Furthermore, it is not necessary to generate the patterns by the actualalgorithm described above, modifications of this algorithm can also beused. It is only important that both encoder and decoder generated (andlater use) the same list of Wedgelet patterns for the encoding anddecoding process.

1.4.2 Minimum Distortion Wedgelet Search

Based on the lookup lists described above, the best approximation of thesignal of a block by a Wedgelet partition can be found by a searchalgorithm. For Wedgelet-based coding algorithms the best approximationmay be understood as the Wedgelet model that causes the minimumdistortion. In other word, the search tries to find the best matchingWedgelet partition pattern for the given block. The search utilizes thederived pattern list, which contains all possible Wedgelet partitionpatterns for a given block size (see section 1.4.1 for details). Theselists help to limit the processing time of the search, as the patternsdon't need to be generated again, each time a minimum distortionWedgelet search is carried out. Each search step may consist of thefollowing steps:

-   -   Calculation of the CPV values from the given partition pattern        and the original block signal.    -   Calculation of the distortion D_(W,cur) between original block        signal and Wedgelet model.    -   Evaluation of D_(W, cur)<D_(W,min): if true, update minimum        distortion Wedgelet information, by setting D_(W,min)=D_(W,cur)        and storing the list index of the current partition pattern.

Instead of the distortion, a Lagrangian cost measure can be used forfinding the used Wedgelet pattern. The Lagrangian const measure is aweighted sum D+λ−R that weights the distortion D obtained by aparticular wedgelet pattern with the rate R that is necessitated fortransmitting the associated parameters given a Lagrangian multiplier λ.

Different strategies are possible for the search algorithm, ranging froman exhaustive search to fast search strategies. Exhaustive search meansthat all elements of the Wedgelet pattern list are successively testedfor minimum distortion. This strategy ensures that the global minimum isfound, but for the price of being slow (which is especially importantfor the encoder). Fast search means advanced strategies that reduce thenumber of necessitated search steps. A fast search strategy could forinstance be a successive refinement. In a first phase the minimumdistortion Wedgelet for a subset of partition patterns resulting from alimited number of line start and end positions, e.g. only every fourthborder sample, is searched. In a second phase the start and endpositions would be refined, e.g. by allowing every second border sample,but limiting the range of tested start and end positions to a rangearound the best result of the first phase. By refining the step size inevery cycle, finally the minimum distortion Wedgelet is found. Incontrast to full search, such a fast search strategy only allows findinga local minimum, but the number of Wedgelet patterns to be tested issignificantly lower and consequently the search is faster. Note, thatthe step size of the first phase does not need to be a fixed value, butcan be set adaptively, e.g. as a function of the block size.

The just-discussed index indexing the course of the wedgelet line orwedgelet pattern could be called wedge_full_tab_idx.

2. Contours

Note that although most of the examples in this section use quadraticblocks, Contour block partitions and all related embodiments are notlimited to quadratic blocks, but are rather possible for any rectangularblock size.

2.1. Contour Block Partition

The basic principle of Contour block partitions is to partition the areaof a block 200 into two regions 202 a, 202 b. Unlike for Wedgelet blockpartitions, the separation line 201 between the regions cannot bedescribed by a geometrical formulation. As illustrated by the tworegions labeled with P₁ and P₂ in FIG. 9, the regions of a Contour canbe of arbitrary shape and they are not even required to be connected.

FIG. 9 also illustrates the difference between continuous and discretesignal space for Contour block partitions. Again, only complete samplescan be assigned as part of either of the two regions for the discretesignal space (FIG. 9, right). When the Contour partition information isderived from a discrete reference signal (see section 3.2.2 for details)and not from a geometrical formulation, no assignment problem like forWedgelet block partitions has to be taken into account here.

2.2. Contour Partition Patterns

In conformance with Wedgelet partition patterns (see section 1.2), theContour block partition information may be stored in the form ofpartition patterns. Such a pattern consists of an array of sizeU_(B)×v_(B) and each element contains the binary information whether theaccording sample belongs to region P₁ or P₂. FIG. 10 shows an exampleContour partition pattern, representing the binary region information byblack or white sample color.

2.3. Contour Modeling and Approximation

The principle of approximating the depth signal of a block with by aContour is identical to the Wedgelet concept described in section 1.3.Again, the necessitated information may consist of the two elementspartition information and the partition filling instruction which, inturn, may comprise one constant partition value (CPV) for each of thetwo regions, which may be calculated as the mean value of the originaldepth signal of the corresponding region.

The Contour approximation is illustrated in FIG. 11, where the originaldepth signal of a prediction block 200 is highlighted in order to showits surroundings and is shown enlarged. Again, the partition informationin terms of regions P₁ and P₂ is overlaid with the block first and thenthe CPV is calculated as the mean value of all samples covered by theregion. As the partition information in the example in FIG. 11 matchesthe depth signal quite well, the resulting Contour model with a lowerCPV for region P₁ (darker grey) and a higher CPV for region P₂ (brightergrey) represents a good approximation of the depth block.

3. Block Partition Coding

For using the methods and algorithms described in the previous sectionswithin a coding framework for multi-view video plus depth (MVD) such asthe coding environment of FIGS. 1 to 3, new coding routines or modesshould be defined and the necessitated tools should be implemented inthe encoder and the decoder.

For a hybrid video coder, such as the encoder of FIG. 1, or codingbranch pair 22 _(v/d,1), these tools can be categorized as part ofestimation, prediction, or signaling. Estimation summarizes tools thatare only part of the encoding process as they depend on original inputinformation (e.g. uncompressed pictures). In contrast to that,prediction summarizes tools that are part of the encoding and decodingprocess, as they only rely on transmitted and/or reconstructedinformation (e.g. decoded pictures). Signaling summarizes tools forcoding the information transmitted from the encoder to the decoder inthe bitstream. Consequently, they are necessitated to use an identicalsyntax and identical entropy coding states.

Note that for estimation tools the distortion can be either derived asknown from classic video coding approaches, measuring the differencebetween distorted and original depth signal of the block, e.g. as themean squared error (MSE) or the mean absolute difference (MAD), or asthe distortion in synthesized views, measuring the difference insynthesized views caused by samples that are dislocated due to thedistorted depth signal of the block.

The concepts for irregular block partition coding in accordance withbelow-outlined embodiments can be divided in those for processingpartition information (see sections 3.1 and 3.2) and those forprocessing CPVs (see section 3.3).

3.1. Wedgelet-Based Intra Coding

This section presents two intra coding modes based on Wedgelet blockpartitions (see section 1). Both modes can be combined with the deltaCPV method (see section 3.3.2).

3.1.1 Intra Modeling of Wedgelet Block Partition

The basic principle of this mode is to find the best matching Wedgeletpartition at the encoder and explicitly transmit the partitioninformation in the bitstream. At the decoder the signal of the block isreconstructed using the explicitly transmitted partition information.Consequently, the main tools for this mode are part of estimation andsignaling.

The Wedgelet partition information for this mode is not predicted, butsearched within the estimation process at the encoder. For this purposethe minimum distortion Wedgelet search as described in section 1.4.2 iscarried out, using the original depth signal of the current block as areference. The search results in the best matching Wedgelet partitionwith respect to the distortion method employed.

Reconstructing the block at the decoder, the Wedgelet partitioninformation has to be signaled in the bitstream. This is realized byexplicitly transmitting the position or an index of the accordingpattern in the list (see section 1.4.1). This list index is signaledwith a fixed number of bins. Given a Wedgelet pattern list with Nelements, the index of the used pattern is coded usingfixed-length-codes, or variable length codes, or arithmetic coding(including context-adaptive binary arithmetic coding), or any otherentropy coding method. Advanced methods for signaling the Wedgeletpartition information may include sorting the list based on theprobability of each partition pattern or using an alternativerepresentation of the partition information, e.g. line start and endposition or line start position and gradient.

3.1.2 Intra Prediction of Wedgelet Block Partition

The basic principle of this mode is to predict the Wedgelet partitionfrom information available for previously coded blocks in the samepicture, i.e. intra prediction. For a better approximation, thepredicted partition is refined at the encoder such as, for example, byvarying the line end position. The only transmission of the offset tothe line end position in the bitstream may suffice and at the decoderthe signal of the block may be reconstructed using the partitioninformation that results from combining the predicted partition and thetransmitted refinement information such as the offset. Consequently, themain tools for this mode are part of prediction, estimation, andsignaling.

Prediction of the Wedgelet partition information for this modeinternally works with a Wedgelet representation that consists of thestart position and the gradient of the separation line. For furtherprocessing, namely adapting the line end position offset andreconstructing the signal of the block, the prediction result isconverted in a representation consisting of the line start and endposition. The prediction process of this mode derives the line startposition and the gradient from the information of previously codedblocks, such as the neighbor blocks left and above of the current block.In FIG. 12, merely the current block 210 and the above neighboring block212 are shown. Note that for some blocks one or both of the neighboringblocks are not available. In such a case the processing for this mode iseither skipped or continued with setting the missing information tomeaningful default values.

As illustrated in FIG. 12, two main concepts are distinguished forpredicting the Wedgelet partition information in accordance with thepresently suggested embodiment. The first concept covers the case whenone of the two neighboring reference blocks is of type Wedgelet, shownin the example in FIG. 12, left, where block 212 is exemplarily subjectto wedgelet partitioning. The second concept covers the case when thetwo neighboring reference blocks are not of type Wedgelet, but of typeintra direction, which may be the default intra coding type, shown inthe example in FIG. 12, right, where block 212 is exemplarily subject tointra coding.

If the reference block 212 is of type Wedgelet, the prediction processmay work as follows: According to FIG. 12, left, the gradient m_(ref) ofthe reference Wedgelet is derived from the start position S_(ref) andthe end position E_(ref) in a first step. The principle of this conceptis to continue the reference Wedgelet, i.e. the wedgelet separation line201′, in the current block 210, which is only possible if thecontinuation of the separation line 201′ of the reference Wedgelet 212actually intersects the current block 210. Therefore, the next step isto check whether it is possible to continue the reference Wedgelet. Theexample in FIG. 12, left, shows a scenario where it is possible, but ifthe start and end position of the reference Wedgelet would be located onleft and right edge of the block, the continuation of the line would notintersect the block below. In case the check is positive, the startposition S_(p) and the end position E_(p) are predicted in a final step.As the gradient m_(p) is equal to m_(ref) by definition, the positionsare simply calculated as the intersection points of the continued linewith block border samples.

If the reference block 212 is of type intra direction, the predictionprocess may work as follows: According to FIG. 12, right, the gradientm_(ref) of the reference block 212 is derived from the intra predictiondirection 214 in a first step. In case of the intra direction 214 onlybeing provided in the form of an abstract index, a mapping or conversionfunction may be necessitated for achieving the gradient m_(ref). Unlikethe concept for predicting from a reference block 212 of type Wedgelet,no separation line information is provided by a reference block 212 oftype intra direction. Consequently, the start position S_(p) is derivedfrom information that is also available at the decoder, namely theadjacent samples of the left and above neighboring block. They are shownhatched in FIG. 12, right. The density of hatching shall represent thevalue of the neighboring samples. As illustrated in FIG. 12, right, fromthese adjacent samples the one adjoining the pair of neighboring sampleswith the maximum slope is selected as the start position Sp. Here, slopeis understood as the absolute difference of the values of twoconsecutive samples. For a Wedgelet partition the line start point S_(p)separates the two regions 202 a, 202 b with a different value at oneedge 216 of the block 210. Therefore, the maximum slope point among theadjacent samples of neighboring blocks is the best prediction of S_(p).Regarding the gradient, m_(p) is equal to m_(ref) by definition againand together with S_(p) the end position E_(p) may be calculated as afinal step.

The two presented concepts are complementary. While prediction fromreference blocks of type Wedgelet has better matching partitioninformation, but is not always possible, prediction from referenceblocks of type intra direction is possible, but the partitioninformation is fitting worse. Therefore, it is beneficial to combine thetwo concepts into one prediction mode. For realizing this withoutadditional signaling, the following processing hierarchy may be defined:If the above reference block is of type Wedgelet, try predicting thepartition. Otherwise, if the left reference block is of type Wedgelet,try predicting the partition. Otherwise, predict partition from aboveand left reference information. For the latter, different decisioncriterions for deciding between the above and left direction arepossible, ranging from simply prioritizing above to advanced approachesfor jointly evaluating the directions and the slopes of adjacentsamples. Such advanced criterions might also be applied, if both theabove and left reference blocks are of type Wedgelet.

The line end position offset for refining the Wedgelet partition may notbe predicted, but searched within the estimation process at the encoder.For the search, candidate partitions are generated from the predictedWedgelet partition and an offset value for the line end positionE_(off), as illustrated in FIG. 12. By iterating over a range of offsetvalues and comparing the distortion of the different resulting Wedgeletpartitions, the offset value of the best matching Wedgelet partition isdetermined with respect to the distortion method employed.

For reconstructing the block at the decoder, the line end positionoffset value is to be signaled in the bitstream. Same could be signaledby use of three syntax elements, a first signaling as to whether anyoffset E_(off) is present, i.e. as to whether same is zero, a second onemeaning the sign of the offset, i.e. clockwise or counter-clockwisedeviation, in case of the offset being not zero, and the third denotingthe absolute offset value minus one:

dmm_delta_end_flag, dmm_delta_end_sign_flag, dmm_delta_end_abs_minus1.In pseudo code, these syntax elements could be included as

dmm_delta_end_flag if ( dmm_delta_end_flag) {   dmm_delta_end_abs_minus1    dmm_delta_end_sign_flag}dmm_delta_end_abs_minus1 and dmm_delta_end_sign_flag could be used toderive DmmDeltaEnd, i.e. E_(off), as follows:

-   -   DmmDeltaEnd[x0][y0]=(1-2*dmm_delta_end_sign_flag[x0][y0])*(dmm_delta_end_abs_minus1[x0][y0]+1)

The most probable case is that the offset value is zero. For efficientsignaling, a first bin is sent, which has the function of a flag,indicating whether the offset is zero or not. If the offset is not zero,k+1 additional bins follow for signaling offset values in the range±2^(k), where the first bin represents the sign and the remaining k binsthe absolute value of the offset. For efficient coding k is typically asmall number and might be set adaptively, e.g. depending on the blocksize. The line end position offset can also be transmitted by any otherentropy coding technique, including fixed-length codes, variable-lengthcodes, or arithmetic coding (including context-adaptive binaryarithmetic coding).

3.2. Inter-Component Prediction for Block Partition Coding

This section presents two coding modes based on predicting the partitioninformation from the texture. Both modes can be combined with the deltaCPV method (see section 3.3.2). It is assumed that the textureinformation (i.e., the conventional video picture) is transmitted beforethe associated depth map.

The basic principle of these modes may be described as predicting thepartition information from a texture reference block, either as aWedgelet or as a Contour block partition. This type of prediction mayreferred to as inter-component prediction. Unlike temporal or inter-viewprediction, no motion or disparity compensation is necessary here, asthe texture reference picture shows the scene at the same time and fromthe same perspective. As the partition information is not transmittedfor these modes, the inter-component prediction uses the reconstructedtexture picture as a reference. Depending on the color space used fortexture coding, one or more components of the texture signal are takeninto account for inter-component prediction. For video coding typicallya YUV color space is used. Here, the luma component contains the mostsignificant information for predicting the signal of depth block, i.e.the edges between objects. Thus, a simple inter-component predictionapproach only exploits the information of the luma component whileadvanced approaches additionally take advantage of the chromacomponents, either for a joint prediction or for refining the lumaprediction result.

3.2.1 Texture-Based Prediction of Wedgelet Block Partition

The basic principle of this mode is to predict the Wedgelet partition ofa depth block 210 in the depth map 213 from the texture reference block216. This is realized by searching the best matching Wedgelet partitionfor the reconstructed texture picture, as illustrated in FIG. 13. Forthis purpose the minimum distortion Wedgelet search, as described insection 1.4.2, is carried out, using the reconstructed texture signal215, more specifically the luma block 216 with same position and size asthe depth block 210, as a reference. The resulting Wedgelet partitionpattern 218 is used for prediction 220 of the depth block. In FIG. 13,this is highlighted by the top boxes and for the shown example thepredicted Wedgelet partition (middle) approximates the depth block 210very well. As the described Wedgelet prediction can be performedidentically at the encoder and the decoder, no signaling of partitioninformation is required for this mode.

3.2.2 Texture-Based Prediction of Contour Block Partition

The basic principle of this mode is to predict the Contour partition ofa depth block from the texture reference block. This is realized byderiving the Contour partition 218′ for the reconstructed texturepicture 215, as illustrated in FIG. 10. For this purpose a Contourapproximation, is carried out, using the reconstructed texture signal215, more specifically the luma block 216 with same position and size asthe depth block 210, as a reference. As such a Contour prediction can beperformed identically at the encoder and the decoder, no signaling ofpartition information is required for this mode.

The Contour partition pattern may be generated by calculating the meanvalue of the reference block 216 and setting it as a threshold.Depending on whether the value of a sample in the reference block 216 isbelow or above the threshold, the according position is either marked aspart of region P₁ or P₂ in the partition pattern 218′. The resultingContour partition pattern 218′ is used for prediction 220 of the depthblock 210. In FIG. 13, this is highlighted by bottom boxes and for theshown example the predicted Contour partition (middle) 218′ approximatesthe depth block 210 very well. However, the threshold approachpotentially leads to frayed patterns with many isolated small parts,which does not approximate the depth signal well. For improving theconsistency of the Contour patterns, the deviation process can beextended, e.g. by filtering or segmentation approaches.

The binary partition pattern defining the contour partition pattern,dmmWedgeletPattern[x, y], with (x,y) with x, y=0 . . . nT−1 denoting thesample positions within the block to be partitioned, may be derived fromthe luma samples of the collocated texture video blockvideoLumaSamples[x, y], with x, y=0 . . . nT−1, as follows.

A threshold tH is derived as:

tH=sumDC/(nT*nT), with sumDC+=videoLumaSamples[x, y] for x, y=0 . . .nT−1

The pattern values are set as:

-   -   If videoLumaSamples[x, y] is larger than tH, the following        applies:    -   dmmWedgeletPattern[x, y]=1    -   Otherwise, the following applies:    -   dmmWedgeletPattern[x, y]=0

3.3. CPV Coding

Concepts for CPV coding are presented in this section. They can beidentically applied to all four modes for predicting or estimating blockpartition information (see sections 3.1 and 3.2), as both partitiontypes, Wedgelet and Contour, have two partition regions with a constantvalue by definition. Consequently, CPV processing does not need todistinguish between partition types or coding modes, but rather assumesthat a partition pattern is given for the current depth block.

3.3.1 Prediction CPVs

For a better understanding of CPV prediction, three types of CPV aredistinguished, which are: original CPV, predicted CPV, and delta CPV.The relation between them is schematically illustrated in FIG. 14,right, for the cross section of the block (dotted line 230 in FIG. 14,left). Here, the line 232 represents the original signal of the block200 along line 230. According to the description in sections 1.3 and 2.3the original CPVs (lines 234 and 236 in FIG. 14, right) are calculatedas the mean value of the signal covered by the corresponding region P1and P₂, respectively.

Original CPVs W_(orig,P1) and W_(orig,P2) lead to the best approximationof the original signal (left in FIG. 14, or line 232) for a given blockpartition, but as the original signal is not available at the decoder,it would be necessitated to transmit the values in the bit stream. Thiswould be quite expensive in terms of bit rate and can be avoided byadopting the principle of prediction for CPVs. In contrast to originalCPVs, predicted CPVs are derived from information that is also availableat the decoder, namely the adjacent samples of the left and aboveneighboring block, as illustrated on the hatched samples 203 in FIG. 14,left. Here, the adjacent samples are marked grey and the predicted CPVfor each region of the given partition pattern results from calculatingthe mean value of those samples that adjoin the corresponding region(lines 238 and 240 in FIG. 14, left). Note that the left or aboveneighboring block is not always available. In such a case, therespective adjacent samples may be set to a default value.

In FIG. 14, right, the predicted CPVs W_(pred,P1) and W_(pred,P2) arerepresented by lines 238 and 240 and the illustration highlights thatthe original and the predicted CPVs may differ significantly. In factthe difference ΔW_(P1) and ΔW_(P2) between original and predicted valuesdepends on the similarity between the original signal 232 of the currentblock 200 and the border signal of reconstructed neighboring blocksshown on the hatched samples 203. This difference is defined as thedelta CPV of the corresponding region. This means, that if the delta CPVΔW_(P1) and ΔW_(P2) is estimated at the encoder and transmitted in thebit stream, it is possible to reconstruct the original CPV at thedecoder by adding the delta CPV to the predicted CPV. Only transmittingthe delta instead of the original values leads to a significantreduction of the bit rate necessitated.

The predicted constant partition values CPVs could be calleddmmPredPartitionDC1 and dmmPredPartitionDC2 and derived from neighboringsamples p[x, y] as follows. In the following, dmmWedgeletPattern denotesthe partitioning of the current block encompassing samples (x,y) withexemplarily, x,y=0 . . . nT−1. That is, sample positions neighboring theupper edge are located at (x,−1) with x=0 . . . nT−1, and samplepositions neighboring the left edge are located at (−1,y) with y=0 . . .nT−1. The already reconstructed neighboring sample values are denotedp[x,y]. sumPredDC2, sumPredDC1, numSamplesPredDC2 and numSamplesPredDC1are set to zero at the beginning:

For x=0 . . . nT−1 the above neighboring samples are summed up as:

-   -   If dmmWedgeletPattern[x, 0] is equal to 1 (partition P1, for        instance), the following applies:        -   sumPredDC2+=p[x,−1] and numSamplesPredDC2+=1    -   Otherwise (partition P2, for instance), the following applies:        -   sumPredDC1+=p[x,−1] and numSamplesPredDC1+=1

For y=0 . . . nT−1 the left neighboring samples are summed up as:

-   -   If dmmWedgeletPattern[0, y] is equal to 1, the following        applies:        -   sumPredDC2+=p[−1, y] and numSamplesPredDC2+=1    -   Otherwise, the following applies:        -   sumPredDC1+=p[−1, y] and numSamplesPredDC1+=1

The predicted constant partition values are derived as follows.

-   -   If numSamplesPredDC1 is equal to 0, the following applies:        -   dmmPredPartitionDC1=1<<(BitDepth_(Y)−1)    -   Otherwise, the following applies:        -   dmmPredPartitionDC1=sumPredDC1/numSamplesPredDC1    -   If numSamplesPredDC2 is equal to 0, the following applies:        -   dmmPredPartitionDC2=1<<(BitDepth_(Y)−1)    -   Otherwise, the following applies:        -   dmmPredPartitionDC2=sumPredDC2/numSamplesPredDC2

3.3.2 Quantization and Adaptation of Delta CPVs

Based on the principle of CPV prediction, a concept for efficientprocessing of delta CPVs is introduced in this section. Transmitting thedelta CPVs in the bitstream serves the purpose of reducing thedistortion of the reconstructed signal for block partition coding.However, the bit rate necessitated for signaling the delta CPV valuesdelimits the benefit of this approach, as the difference betweenoriginal and predicted signal is also covered by transform coding of theresiduum. Therefore, quantization of the delta CPVs may be introduced asfollows: the values are linearly quantized after estimation at theencoder and de-quantized before reconstruction at the decoder.Transmitting quantized delta CPVs has the advantage that the bit rate isreduced, while the signal reconstructed from de-quantized values onlydiffers slightly from the best possible approximation. In consequencethis leads to lower rate-distortion cost compared to the case withoutquantization. Regarding the step size of the linear quantization, theperformance can be further improved by applying a principle well knownfrom transform coding, namely defining the quantization step size as afunction of the QP and not as a fixed value. Setting the quantizationstep size for the delta CPVs as q_(ΔCPV)=2^(QP/10) with1≤q_(ΔCPV)≤(ΔCPV)/2 turned out to be efficient and robust.

A possible signaling of the delta CPVs in the bitstream for the tworegions of a partitioned block could be construed as follows:

-   -   dmm_dc_1_abs[x0+i][y0+i]    -   dmm_dc_1_sign_flag[x0+i][y0+i]    -   dmm_dc_2_abs[x0+i][y0+i]    -   dmm_dc_2_sign_flag[x0+i][y0+i]

The transmission on the bitstream for a certain block could be madedependent on a syntax element DmmDeltaFlag, explicitly transmitted orderived from some coding mode syntax element.

dmm_dc-1_abs, dmm_dc-1_sign_flag, dmm_dc-2_abs, dmm_dc-2_sign_flag couldbe used to derive DmmQuantOffsetDC1 and DmmQuantOffsetDC2 values asfollows:

-   -   DmmQuantOffsetDC1[x0][y0]=(1-2*dmm-dc-1_sign_flag[x0][y0])*dmm-dc-1_abs[x0][y0]    -   DmmQuantOffsetDC2[x0][y0]=(1-2*dmm-dc-2        sign_flag[x0][y0])*dmm-dc-2_abs[x0][y0]

The de-quantized offsets dmmOffsetDC1 and dmmOffsetDC2 may be derivedfrom DmmQuantOffsetDC1 and DmmQuantOffsetDC2 as follows.

-   -   dmmOffsetDC1=DmmQuantOffsetDC1*Clip3(1,(1<<BitDepth_(Y))−1,        2(^(QP′) _(Y)/¹⁰)−²)    -   dmmOffsetDC2=DmmQuantOffsetDC2*Clip3(1,(1<<BitDepth_(Y))−1,        2(^(QP′) _(Y)/¹⁰)−²)

BitDepth_(Y) may be the bitdepth at which DmmQuantOffsetDC1 andDmmQuantOffsetDC2 are internally, within Encoder and Decoder,represented, and QP′ may be the just-mentioned quantization parameter QPinvolved in coding transform coefficient levels of the predictionresidual of the current slice, for example.

The constant partition values CPVs are then obtainable by adding thedequantized offsets to the predicted CPVs:

-   -   For the first partition: dmmPredPartitionDC1+dmmOffsetDC1    -   For the second partition: dmmPredPartitionDC2+dmmOffsetDC2

As already mentioned at the beginning of section 3, the distortion forestimation tools can be measured in two different ways. Regarding deltaCPVs, these distortion methods strongly affect the estimation process.In case the distortion is measured as the difference between distortedand original depth signal of the block, the estimation process searchesthe closest approximation of the original CPVs by simply calculating andquantizing the delta CPVs as described above. In case the distortion ismeasured for synthesized views, the estimation process can be extendedfor better adapting the delta CPVs to the quality of synthesized views.This is based on the fact that those delta CPVs that lead to the bestapproximation of the original CPVs not necessarily lead to the bestsynthesized view quality. For finding the delta CPVs that lead to thebest synthesized view quality, the estimation process is extended by aminimum distortion search (cp. Section 1.4.2), which iterates over allpossible delta CPV combinations for the two partitions. For the sake ofefficient processing and signaling the range of tested values can belimited. The search results in the combination of delta CPVs that causesthe minimum distortion in synthesized views and for transmission thesevalues are finally quantized.

Note that the delta CPV method potentially enables skipping thetransformation/quantization and transmission of the (remaining)residuum. Due to a close approximation of the original or optimum depthsignal, respectively, the impact of omitting the residuum is limited,especially if evaluated with respect to the quality of rendered views.

4. Coding of Modes 4.1. Mode Signaling

In the encoding process, one mode is selected for every block throughrate-distortion optimization and the mode information is signaled in thebitstream such as, for example, prior to the partition and CPVinformation. According to section 3 the following four block partitionmodes may be defined (in addition to non-irregular partitioning modes,for example):

-   -   Wedgelet_ModelIntra: Intra modeling of Wedgelet block partition        (see section 3.1.1)    -   Wedgelet_PredIntra: Intra prediction of Wedgelet block partition        (see section 3.1.2)    -   Wedgelet_PredTexture: Texture-based prediction of Wedgelet block        partition (see section 3.2.1)    -   Contour_PredTexture: Texture-based prediction of Contour block        partition (see section 3.2.2)

Each of the four modes can be applied with or without the method fordelta CPV processing (see section 3.3.2), resulting in eight differentmode_IDs for signaling the decoder, which type of processing has to beapplied for prediction and reconstruction of the block.

If the block partition modes introduced above are implemented as anadditional set of block coding modes into an existing coding frameworksuch as the one of FIGS. 1 to 3, an additional flag prior to the modeinformation may be transmitted in the bit stream, signaling whether ablock partition mode is used or not. In case this flag is not set, thenormal block coding mode signaling follows. Otherwise, a mode_ID issignaled, which specifies the actual block partition mode and if deltaCPVs are also transmitted or not. In the bitstream the mode_ID isrepresented through three bins.

4.2. Mode Pre-Selection

The idea behind mode pre-selection is to reduce the processing andsignaling effort for block partition coding (see section 3), byimplementing concepts that exclude modes which are very unlikely to beselected for the current block.

The first mode pre-selection concepts disables modes whose probabilityis very low for small block sizes. This means that in most cases thedistortion is high compared to the rate necessitated for signaling themode information. Among the four modes defined in section 4.1 thisapplies to Wedgelet_Predlntra and Contour_PredTexture. Based on astatistical analysis, these two modes are disabled for block sizes 4×4and smaller.

The second mode pre-selection concept applies to the two modes based oninter-component prediction, namely Wedgelet_PredTexture andContour_PredTexture. The idea behind this concept is to adaptivelyexclude these modes, if it is very unlikely that a meaningful blockpartition pattern can be derived from the texture reference block. Suchblocks are characterized by being relatively plane without significantedges and contours. For identifying these blocks, the variance of thetexture reference block is analyzed. The criterion for disabling the twomentioned modes is that the variance is below a certain threshold. Thismode pre-selection method is implemented as follows: The variance ismeasured as the mean absolute error (MAE) between the luma samples andthe mean value of the reference block (see 216 in FIG. 13). Instead of afixed value, the threshold is set as a function of the quantizationparameter (QP). Based on the results of a statistical analysis of MAEvalues, the threshold is set as tMAz(QP)=2/QP, which has the effect,that these two modes are excluded for more blocks, if the QP is higherand vice versa.

FIG. 15 shows a visualization of this mode pre-selection method, withdetails for two texture luma blocks 250 and 250 ₂ and the absolutedifferences versus the mean value on the right at 252 ₁ and 252 ₂,respectively. Block 250 ₁ has a very plane spatial sample valueappearance with nearly no structure, which is reflected by a very lowvariance. As no meaningful partition information could be predicted fromthis block 250 ₁, the modes Wedgelet_PredTexture and Contour_PredTextureare not considered. In contrast to that block 250 ₂ has a high variance,resulting from significant edges and contours. Thus, the two modes areconsidered, as it is likely that the partition information derived fromblock 250 ₂ is a good predictor for the partition of the according depthblock.

TABLE 1 Modes according to preselection decisions. limitation: blocksize off on off on limitation: texture ref. variance off off on onWedgelet_ModelIntra + delta x x x x Wedgelet_ModelIntra CPVs x x x xWedgelet_PredIntra + delta x x Wedgelet_PredIntra CPVs x xWedgelet_PredTexture x x Wedgelet_PredTexture + delta CPVs x xContour_PredTexture + delta x Contour_PredTexture CPVs x number ofmode_IDs 8 4 4 2 number of bins 3 2 2 1

Table 1 summarizes the effects of the two mode pre-selection concepts onthe available modes. By excluding certain modes, the number of mode_IDsthat have to be signaled in the bitstream decreases. The table showsthat the two methods can be combined in an efficient way, as each methodreduces the number of bins necessitated for signaling the mode_ID by oneand the combination of both modes reduces the number of bins by two.

5. Generalizations

After having described several possible irregular partitioning modes,their conceptual subdivision into bi-segmentation determination (see 3.1and 3.2) on the one hand and coding parameter coding for the resultingtwo partitions (see 3.3) on the other hand, as well as their possibleemployment in a coding framework and the description of a possiblecoding environment to which such modes could be additionally beprovided, the resulting embodiments for respective decoders and encodersshall be described, partially in more generic terms. In particular, thefollowing sections highlight specific advantageous details outlinedabove and explain how these details may be used within decoders andencoders in a sense more generic than described above. In particular, aswill be outlined below, some of the advantageous aspects used in theabove modes, may be exploited individually.

5.1. Wedgelet Separation Line Continuation Across Block Borders

As became clear from the above discussion, the use of wedgeletpartitioning forms a possible compromise between signaling overhead forsignaling the partitioning on the one hand, and the amount of varietyachievable by the irregular partitioning on the other hand.Nevertheless, a remarkable amount of side information data would benecessitated in order to explicitly transmit the partitioninginformation, i.e. the position of the wedgelet separation line such as,for example, by using indexing of the position of the wedgeletseparation line such as, for example, in accordance with the conceptoutlined above with respect to section 3.1.1.

Accordingly, wedgelet separation line continuation across block bordersforms one possible way of solving the just outlined problem. The abovedescription in section 3.1.2 explained a specific example for takingadvantage of this problem's solution. More generically, however, inexploiting the idea of wedgelet separation line continuation over blockborders, a decoder may, in accordance with an embodiment of the presentinvention, be constructed as outlined below with respect to FIG. 16.Nevertheless, all the details described in section 3.1.2 and the othersections among 3 to 4 are to be understood as possible realizationdetails, which may be combined with the description presented belowindividually.

The decoder of FIG. 16 is generally indicated with reference sign 300and is configured to reconstruct a sample array 302 from a data stream304. The decoder is configured to perform the reconstruction byblock-based decoding. For example, the sample array 302 may be part of asequence of sample arrays and the decoder 300 may be implemented as ablock-based hybrid decoder supporting different coding modes for eachblock 304. The sample array may be any spatially sampled informationsuch as, for example, texture or depth maps. For example, the decoder300 of FIG. 16 may be implemented so as to reconstruct one viewincluding texture/video and depth/disparity maps representing the samplearray 302. Insofar, the decoder 300 may be implemented as the pair ofdecoding branches 106 _(d,1) plus 106 _(v,1) or may be implementedaccording to decoding branch 106 _(d,1) individually. That is, decoder300 may be configured to reconstruct the sample array 302 using codingmodes such as intra prediction, temporal (motion compensated) predictionand/or inter-view (disparity compensated) prediction, with and withoutresidual coding of the prediction residual. The coding modes may, forexample, also comprise an explicit wedgelet coding mode according towhich for a respective block, the position of its wedgelet separationline is transmitted explicitly within data stream 304, such as the modeoutlined in section 3.1.1.

In any case, this decoder 300 is configured such that same performs fora current block 210, such as a block for which a predetermined codingmode option is signaled within data stream 304, the steps outlined now.The functionalities involved in these steps may be integrated withinintra-prediction module 36 or intra-prediction module and exchangemodule 52.

The steps performed by decoder 300 for a block of a respective mode area wedgelet separation line position prediction 306 followed by aposition refinement 308 and a decoding 310. In particular, the decoderof FIG. 16 is configured to predict in step 306 a position 312 of awedgelet separation line within block 210 of the sample array 302depending on a wedgelet separation line 201′ of a neighboring block 212of block 210 such that the wedgelet separation line at the predictedposition 312 forms an extension or continuation of the wedgeletseparation line 201′ of the neighboring block 212 into the current block210. Again, decoder 300 may have derived the position of the wedgeletseparation line 201′ of the neighboring block 212 by respective explicitsignaling for block 212 from data stream 304 or by some other codingoption, such as by edge detection within a texture sample array, whichsample array 302 belongs to or the like. Other possibilities have beendescribed above and will be further described below.

As described above, the wedgelet separation line of block 210, theposition 312 of which is predicted in 306, may be a straight line as itwas the case with the above description in section 3.1.2. However,alternatively, the lines may be defined more generally, e.g. using asequence of sample positions hops, i.e. a sequence of symbols eachdefining the next pixels in line, belonging the separation line. Thelines may have a predetermined analytically determined curvature whichmay also be predicted from line 201′ or may be derived from some otherpreviously processed portion of data stream 304.

In particular, the prediction 306 may be configured such that,afterwards, the wedgelet separation line of block 210 is preliminarilydetermined with respect to the general extension direction as well asthe position lateral to the general extension direction of the wedgeletseparation line. In case of a curved line, curve fitting using, forexample, a polynomial function, may be used to extrapolate theseparation line of block 212 and locate block's 210 separation line,respectively. In case of a straight line, slope and position in adirection lateral to the wedgelet separation line is determined.

With regard to the prediction 306, it should also be mentioned that theneighborhood and the extension do not necessarily have to be defined inspatial terms. Rather, blocks 210 and 212 could also be temporallyneighboring. For example, block 212 could be the co-located block of asample array of a sample array sequence temporally neighboring thesample array 302. In that case, the extension of the wedgelet separationline 201 into block 210 would be a “temporal continuation”.

An explicit possibility how the prediction 306 could be performed hasbeen outlined above in section 3.1.2, which description is referred tohere. The position refinement 308 is for refining the predicted position312. That is, decoder 300 is configured to, in the position refinement308, refine the predicted position 312 of the wedgelet separation line301 of block 210 using refinement information signaled within the datastream 304. Thereby, the wedgelet separation line 201 as refined dividesblock 210 into first and second wedgelet partitions 202 a and 202 b.

As described above, the decoder 300 may be configured such that thewedgelet separation line 201 at the predicted position 312 forms aspatial co-linear extension of the wedgelet separation line 201′ of theneighboring block 212, and the refinement may be restricted such that astart position 314 of the wedgelet separation line of the predeterminedblock 210, adjoining the neighboring block 212, is maintained relativeto the predicted position 312, irrespective of the refinementinformation. That is, in case of a straight wedgelet separation line,merely its slope may be refined, while the starting point of thewedgelet separation line 201 at the edge 316 of block 210 separatingblocks 210 and 212, remains unchanged. For example, the offset of theopposite end 318 of wedgelet separation line 201, i.e. of the endposition of wedgelet separation line 201, along the circumference ofblock 210 from the end position 320 in accordance with a predictedwedgelet separation line position 312 may be signaled within the datastream 304 as described above with respect to section 3.1.2.

In section 3.1.2, the offset was denoted as E_(off). As described inthis section, the decoder 300 may be configured to extract therefinement information from the data stream using entropy decoding wheredifferent possible offsets from the direct extension sample position 320along the circumference of block 210, measured in units of a sampleposition pitch along the circumference direction, have a probabilityestimate associated therewith which monotonically increases from greateroffsets to smaller offsets, so that smaller offsets have a higherprobability associated therewith than greater offsets. For example, theVLC codeword length may monotonically decrease.

As described also above, three syntax elements may be used to transmitE_(off), a first signaling as to whether any offset E_(off) is present,i.e. as to whether same is zero, a second one meaning the sign of theoffset, i.e. clockwise or counter-clockwise deviation, in case of theoffset being not zero, and the third denoting the absolute offset valueminus one: dmm_delta_end_flag, dmm_delta_end_sign_flag,dmm_delta_end_abs_minus1. In pseudo code, these syntax elements could beincluded as

dmm_delta_end_flag if ( dmm_delta_end_flag) {   dmm_delta_end_abs_minus1    dmm_delta_end_sign_flag}DmmDeltaEnd, i.e. E_(off), as follows:

-   -   DmmDeltaEnd[x0][y0]=(1-2*dmm_delta_end_sign_flag[x0][y0])*(dmm_delta_end_abs_minus1[x0][y0]+1)

Then, decoder 300 is configured to, in the decoding 310, decode thepredetermined block 210 in units of the first and second wedgeletpartitions 202 a and 202 b. In the description brought forward above insections 3 and 4, especially section 4, the decoding 310 involved aprediction of the current block 210 by assigning a first constantpartition value W_(pred,P1) to samples of the sample array positionwithin the first wedgelet partition 202 a and a second constantpartition value W_(pred,P2) to samples of the sample array positionwithin the second wedgelet partition 202 b. The advantage of thisimplementation of the decoding procedure 310 is that the amount of sideinformation may be kept low. In particular, this possible implementationis especially advantageous in case of the kind of information conveyedby the sample array having the above-outlined property of being composedof relatively flat value plateaus with steep edges therebetween, such asin case of depth maps. However, it would even be possible that thedecoder assigned other coding parameters individually to the wedgeletpartitions 202 a and 202 b. For example, motion and/or disparitycompensated prediction may be applied individually to partitions 202 aand 202 b in decoding 310 thereby obtaining respective motion and/ordisparity parameters individually for partitions 202 a and 202 b such asindividual vectors. Alternatively, partitions 202 a and 202 b may beindividually be intra-coded in decoding 306 such as by individuallyapplying a respective intra coding direction onto same.

According to FIG. 16, the following information may be present in datastream for block 210: 1) the coding option identifier having therespective predetermined state triggering the steps 306-310, 2) therefinement information such as the end position offset, 3) optionally,coding parameters—such as CPV or CPV residual—for one or both partitions202 a, 202 b—optional, because same may be allowed to bepredicted—spatially or temporally from neighboring samples/blocks, 4)optionally, coding parameter residual such as DeltaCPV.

Moreover, the decoder 300 of FIG. 16 may be configured such that thecoding mode realized by procedures 306 to 310 is merely a default codingmode option among two coding mode options triggered by a respectivecommon predetermined value of a respective coding option identifierwithin data stream 304. For example, the decoder 300 of FIG. 16 could beconfigured to retrieve a coding option identifier from the data stream304 with, if the coding option identifier has a predetermined value,checking whether any of a set of candidate blocks neighboring thepredetermined block has a wedgelet separation line extending into block210. For example, the candidate blocks may encompass the spatiallyneighboring blocks 304 of sample array 302 which precede the currentblock 210 in a coding order—or decoding order—applied by the decoder 300in decoding blocks 304 of sample array 302. For example, the codingorder may scan the blocks 304 row-wise from left to right, top tobottom, and in that case the candidate blocks may encompass theimmediately neighboring block to the left of the current block 210 andthe immediately neighboring block to the top of the current block 210such as block 212. If the check reveals that there is such a wedgeletblock among the set of candidate blocks, decoder 300 may perform theprediction 306, the refinement 308 and the decoding 310 in an unmodifiedmanner. If not, however, decoder 300 may perform the prediction 306differently. As described above in section 3.1.2 and as will be outlinedin more detail with respect to the next section, decoder 300 may then beconfigured to predict the position of the wedgelet separation line 201within the current block 210 by setting an extension direction of thewedgelet separation line 201 within the current block 210 depending onreconstructed neighboring samples neighboring the current block 210 ordepending on an intra prediction direction of one or moreintra-predicted blocks of the candidate blocks. As far as the possibleimplementations for the prediction of the constant partition values inthe decoding 310 are concerned, reference is made to the above and belowexplanations.

Further, it should be noted that a specific advantage results if thewedgelet separation line continuation across block borders is combinedwith a coding mode which enables more freedom in the bi-segmentation ofthe current block, such as a contour mode as outlined above anddescribed further below. To be more precise, decoder 300 may beconfigured to support the mode realized by blocks 306 to 310 as well asa contour partitioning mode, thereby enabling adapting the codingoverhead appropriately to the blocks' needs.

In any case, the block as decoded/reconstructed by procedures 306 to310, may serve as a reference in a prediction loop of decoder 300. Thatis, the prediction result in case of using the bi-valued prediction, mayserve as a reference, for example, for motion and/or disparitycompensated prediction. Moreover, the reconstructed values obtained bythe decoding 310, may serve as spatial neighboring samples in intrapredicting any of the blocks 304 of sample array 302 following indecoding order.

FIG. 17 shows a possible encoder fitting to the decoder of FIG. 16. Inparticular, FIG. 17 shows an encoder 330 for encoding a sample arrayinto a data stream configured to predict a position of a wedgeletseparation line within a predetermined block of the sample arraydepending on a wedgelet separation line of a neighboring block of thepredetermined block such that the wedgelet separation line at thepredicted position forms an extension of the wedgelet separation line ofthe neighboring block into the predetermined block. This functionalityis shown at 332. Further, the decoder 330 has the functionality 334 torefine the predicted position of the wedgelet separation line usingrefinement information, the wedgelet separation line of thepredetermined block dividing the predetermined block into first andsecond wedgelet partitions. The encoder 330 also has an insertionfunctionality 336 according to which the refinement information isinserted into the data stream and an encoding functionality according towhich encoder 330 encodes the predetermined block in units of the firstand second wedgelet partitions.

5.2. Wedgelet Separation Line Extension Direction Prediction from anIntra Prediction Direction of a Neighboring Block

As described above, even wedgelet-based block partitioning necessitatesa remarkable amount of side information in order to inform the decodingside on the position of the wedgelet separation line.

An idea that the below-outlined embodiments are based on is that theintra prediction direction of a neighboring, intra-predicted block maybe used in order to predict the extension direction of the wedgeletseparation line of a current block, thereby reducing the sideinformation rate necessitated in order to convey the partitioninginformation.

In the above description, section 3.1.2 showed a possible implementationof the below-outlined embodiments which, in turn, are described in moregeneric terms so as to not be restricted to the conglomeration ofirregular partitioning modes outlined above in sections 3 and 4. Rather,the just mentioned idea may be advantageously used independent from theother details described in section 3.1.2, as described in more detailbelow. Nevertheless, all the details described in section 3.1.2 and theother sections are to be understood as possible realization details,which may be combined with the description presented below individually.

Accordingly, FIG. 18 shows an embodiment for a decoder 400, whichexploits the just-outlined idea and may be implemented as describedabove with respect to section 3.1.2 and/or FIGS. 1 to 3 as far aspossible additional functionalities are concerned. That is, the decoder400 of FIG. 18 is configured to reconstruct a sample array 302 from adata stream 304. Generally, decoder 400 of FIG. 18 may be implemented asset out above in section 5 with respect to decoder 300 of FIG. 16,except for the coding mode defined by the functionalities 306 to 310,which is optional for the decoder of FIG. 18. That is, the decoder 400of FIG. 18 may operate to reconstruct the sample array 302 of FIG. 18 byblock-based decoding, such as block-based hybrid decoding. Among thecoding modes available for blocks 303 of sample array 302, there is anintra prediction mode further outlined with respect to functionalitymodule 402 of decoder 400. Just as it is the case with decoder 300 ofFIG. 18, the subdivision of sample array 302 into blocks 303 may befixed by default, or may be signaled within data stream 304 byrespective subdivision information. In particular, decoder 400 of FIG.18 may be constructed as outlined above with respect to FIGS. 1 to 3,namely like the decoder of FIG. 3 or any of the view decoders such asthe pair of coding branches 106 _(v/d,1), or merely as a depth decodersuch as 106 _(d,1).

In particular, the decoder 400 of FIG. 18 has a functionality 402according to which a first block 212 of the sample array 302 ispredicted using intra prediction. For example, the intra prediction modeis signaled within data stream 304 for block 212. Decoder 400 may beconfigured to perform the intra prediction 402 by filling the firstblock 212 by copying reconstructed values of samples 404 of the samplearray 302, neighboring the first block 212 along an intra predictiondirection 214 into the first block 212. The intra prediction direction214 may also be signaled within data stream 304 for block 212, such asby indexing one of several possible directions. Alternatively, the intraprediction direction 214 of block 212 itself may be subject toprediction. See, for example, the description of FIGS. 1 to 3 whereintra predictor 36 of decoding branch 106 _(d,1) could be configured toperform step 402. To be more precise, the neighboring samples 404 maybelong to blocks 303 of the sample array 302 which have already beenpassed in decoding order by decoder 400 so that their reconstruction isalready available, including the reconstructed values of the neighboringsamples 404 neighboring block 212. As described above, various codingmodes may be have been used by decoder 400 to reconstruct thesepreceding blocks, preceding in decoding order.

Further, the decoder 400 of FIG. 18 is configured to predict a position312 of a wedgelet separation line 201 within a second block 210neighboring the first block 212 by setting an extension direction of thewedgelet separation line 201 within the second block 210 depending onthe intra prediction direction 214 of the neighboring block 212, thewedgelet separation line 201 dividing the second block 210 into firstand second wedgelet partitions 202 a and 202 b. For example, the decoder400 of FIG. 18 may be configured to set the extension direction of thewedgelet separation line 201 to be equal to the intra predictiondirection 214 as far as possible with respect to a quantization of arepresentation of the extension direction of the wedgelet separationline 201. In case of a straight separation line, the extension directionsimply corresponds to the line's slope. In case of curved separationlines, the intra prediction direction may, for example, adopted as thelocal slope of the current block's separation line at the border to theneighboring block. For example, the decoder 400 of FIG. 18 chooses theextension direction among a set of possible extension directions whichforms the best approximation of the intra prediction direction 214.

Thus, in the prediction 404, the decoder 400 predicts the position 312of the wedgelet separation line 201 of the current block 210 at least asfar as the extension direction thereof is concerned. The derivation ofthe position of the wedgelet separation line 201 of the second block 210may be finalized with leaving the extension direction 408 unmodified.For example, although it was described in section 3.1.2 that aprediction of a starting point 314 of the wedgelet separation line 201may be performed by decoder 400 in deriving the wedgelet separation lineposition in step 406, decoder 400 may alternatively be configured toderive this starting point 314 by explicit signaling within data stream304. Moreover, decoder 400 of FIG. 18 could be configured to spatiallyplace the wedgelet separation line 201 in the derivation 406 in adirection lateral to the extension direction 316 such as undermaintenance of the extension direction 316, parallel to the extensiondirection 316, by temporally predicting the distance in the lateraldirection from a co-located wedgelet block in a previously decodedsample array, or by spatially predicting the position in the lateraldirection from another sample array belonging to a different viewcompared to sample array 302.

It is, however, of advantage that the decoder 400, in deriving theposition of the wedgelet separation line 201 within the second block 210of the sample array 302, places a starting point 314 of the wedgeletseparation line 201 at a position of a maximum change betweenconsecutive ones of a sequence of reconstructed values of samples of aline of samples extending adjacent to the second block 210 along aportion of a circumference of the second block 210. The line of samplesis indicated by reference sign 410 in FIG. 18 with the samples beingsymbolized by small crosses. The line 410 of samples may be restrictedto samples of spatially neighboring blocks being available. In any case,it should be emphasized that the line 410 of samples within which themaximum change is determined, may extend around one of the corners ofrectangular block 210 as shown in FIG. 18. Thus, according to thisprocedure decoder 400 may be configured to place the wedgelet separationline in the derivation 406 so as to start between the neighboringsamples and the sample line 410, where the maximum difference in thereconstructed values exists, in parallel to the extension direction 408.

Accordingly, side information rate is saved since a good prediction hasbeen found to derive the position of the wedgelet separation line 201 byother means than explicit signalization within the data stream 304.

Then, the decoding 412 by decoder 400 takes place according to whichdecoder 400 decodes the second block in units of the first and secondwedgelet partitions 202 a and 202 b just as it was described withrespect to FIG. 16.

Naturally, the decoder 400 of FIG. 18 may be modified to also comprisethe refinement functionality 308 of FIG. 16. Accordingly, an offset ofthe end position 318 of the wedgelet separation line 201 of the currentblock 210 relative to an end position 320 of the position of thewedgelet separation line-which may or may not, as denoted above, berestricted to be straight—as derived in step 406 may be signaled withinthe data stream 304.

As described also above, three syntax elements may be used to transmitsuch an end position offset, E_(off), a first signaling as to whetherany offset E_(off) is present, i.e. as to whether same is zero, a secondone meaning the sign of the offset, i.e. clockwise or counter-clockwisedeviation, in case of the offset being not zero, and the third denotingthe absolute offset value minus one: dmm_delta_end_flag,dmm_delta_end_sign_flag, dmm_delta_end_abs_minus1. In pseudo code, thesesyntax elements could be included as

dmm_delta_end_flag if ( dmm_delta_end_flag) {   dmm_delta_end_abs_minus1    dmm_delta_end_sign_flag}dmm_delta_end_abs_minus1 and dmm_delta_end_sign_flag could be used toderive DmmDeltaEnd, i.e. E_(off), as follows:DmmDeltaEnd[x0][y0]=(1-2*dmm_delta_end_sign_flag[x0][y0])*(dmm_delta_end_abs_minus1[x0][y0]+1)

However, alternative procedure are feasible as well. For example,instead of signaling the end position offset, a direction or angleoffset relative to the extension direction set depending on the intraprediction direction 214 could be signaled within data stream 304 forblock 202.

According to FIG. 18, the following information may be present in datastream for block 210: 1) the coding option identifier having therespective predetermined state triggering the steps 406-412, 2)optionally, refinement information such as an end position offset, 3)optionally, coding parameters-such as CPV or CPV residual—for one orboth partitions 202 a, 202 b—optional, because same may be allowed to bepredicted-spatially or temporally from neighboring samples/blocks, 4)optionally, coding parameter residual such as DeltaCPV.

Regarding the possible modifications of the decoding step 412 relativeto the description of section 3.3, reference is made to the abovedescription of step 310 of FIG. 16.

It goes without saying that the decoder 400 of FIG. 18 may be configuredto treat steps 406 and 412 as a coding mode option that is activated bya coding option identifier within data stream 304, wherein the wedgeletseparation line position derivation 406 forms a subordinate measure forderiving the wedgelet separation line position in case none of a set ofcandidate blocks in the neighborhood of the current block 210 alreadyhas a wedgelet separation line in it, an extension of which continuesinto the current block 210.

FIG. 19 shows an embodiment for an encoder fitting the decoder of FIG.18. The encoder of FIG. 19 is generally indicated at reference sign 430and is configured to encode the sample array into a data stream 304.Internally, the encoder 430 is configured to predict a first block ofthe sample array using the intra prediction in block 432, and the linederivation in accordance with the description of block 406 in FIG. 18 inblock 434. Then, encoder 430 encodes the second block which was thesubject of the line derivation in 434, in units of the first and secondpartitions in encoding block 436.

Naturally, the encoder 430 is, beyond the functionalities shown in FIG.19, configured to operate so as to mirror the functionality of thedecoder of FIG. 18. That is, the encoder 430 may operate block-basedusing, for example, block-based hybrid encoding. Although not explicitlysaid, same also applies with regard to the encoder of FIG. 17 whencompared to the decoder of FIG. 16.

5.3. Wedgelet Separation Line Derivation by Placing the Starting PointThereof According to Reconstructed Values of Neighboring Samples

A further way to reduce the side information necessitated in order toconvey the information on the position of the wedgelet separation lineof wedgelet blocks forms the basis of the embodiment outlined furtherbelow. In particular, the idea is that previously reconstructed samples,i.e. reconstructed values of blocks preceding the current block inaccordance with the coding/decoding order allow for at least aprediction of a correct placement of a starting point of the wedgeletseparation line, namely by placing the starting point of the wedgeletseparation line at a position of a maximum change between consecutiveones of a sequence of reconstructed values of samples of a line ofsamples extending adjacent to the current block along a circumferencethereof. Thus, similar to the possibilities outlined above with respectto sections 5.1 and 5.2, the side information rate necessitated in orderto allow for the decoder to correctly position the wedgelet separationline may be reduced. The idea underlying the embodiment outlined belowwas also exploited in the above description in section 3.1.2, whereaccordingly a possible implementation of the embodiments outlined belowis described.

Accordingly, FIG. 20 shows an embodiment for a decoder 500, whichexploits the just-outlined idea and may be implemented as describedabove with respect to section 3.1.2 and/or FIGS. 1 to 3 as far aspossible additional functionalities are concerned. That is, the decoder500 of FIG. 20 is configured to reconstruct a sample array 302 from adata stream 304. Generally, decoder 500 of FIG. 20 may be implemented asset out above in section 5.1 or 5.2 with respect to decoder 300 of FIG.16, for example, except for the coding mode defined by thefunctionalities 306 to 310, which is optional for the decoder of FIG.18, and with respect to decoder 400 of FIG. 18, for example, except forthe coding mode defined by the functionalities 402, 406 and 412, whichis optional for the decoder of FIG. 20. That is, the decoder 500 of FIG.20 may operate to reconstruct the sample array 302 of FIG. 20 byblock-based decoding, such as block-based hybrid decoding. Just as it isthe case with decoder 300 of FIG. 18, the subdivision of sample array302 into blocks 303 may be fixed by default, or may be signaled withindata stream 304 by respective subdivision information. In particular,decoder 500 of FIG. 20 may be constructed as outlined above with respectto FIGS. 1 to 3, namely like the decoder of FIG. 3 or any of the viewdecoders such as the pair of coding branches 106 _(v/d,1), or merely asa depth decoder such as 106 _(d,1).

Frankly speaking, the decoder of FIG. 20 which is shown at referencesign 500, largely corresponds to the decoder of FIG. 18. However, thefunctionality outlined with regard to FIG. 18 in blocks 402 and 406merely represents optional steps with regard to FIG. 20. Rather, thedecoder 500 of FIG. 20 is configured to derive in step 406′ a positionof a wedgelet separation line 201 within a predetermined block 210 ofthe sample array 302 by placing a starting point 314 of the wedgeletseparation line 201 at a position of a maximum change betweenconsecutive ones of a sequence of reconstructed values of samples of aline 410 of samples extending adjacent to the predetermined block 210along a portion of a circumference of a predetermined block 210, thewedgelet separation line 201 dividing the predetermined block 210 intofirst and second wedgelet partitions 202 a and 202 b. In step 412′, thedecoder 500 then performs the decoding of the resulting partitions 202 aand 202 b in the way outlined above with respect to FIG. 18.

To be more precise, in the derivation 406′, decoder 500 orders thereconstructed values of the samples of the already decoded neighboringblocks of block 210 according to their order of their occurrence whentraversing these samples in a counter clockwise or clockwise direction.A resulting sequence of reconstructed values is illustrated in FIG. 20at 502. As can be seen, the greatest difference between consecutivereconstructed values occurs between the nth and (n+1)th neighboringsamples and accordingly, the decoder of FIG. 20 would place the wedgeletseparation line at the edge 316, to which this pair of neighboringsamples adjoins, between samples of block 210 which, in turn, directlyadjoin this pair of neighboring samples. As outlined above, decoder 500may use a row-wise block scanning direction and accordingly theneighboring samples of sample line 410 may extend along the left-handedge and top edge of block 210. The same could be achieved by using amix of a row-wise scan of tree root blocks which are, in accordance withthe decoding/coding order, scanned row-wise, wherein for each tree rootblock currently visited a quad-tree subdivision is performed, the leafroot blocks of which are scanned in a depth-first traversal order. Whenusing such an order, the likelihood of having a maximum number ofalready reconstructed neighboring samples is increased as compared tousing a breadth-first traversal order.

In the derivation 406′, the decoder 500 of FIG. 20 may use thederivation of the wedgelet separation line extension direction 408 asdescribed with regard to FIG. 18 and in section 3.1.2 as an optionalmanner. Alternatively, the wedgelet separation line extension directionalong which decoder 500 positions the wedgelet separation line 201 ofthe current block 210 may be predicted differently, such as, forexample, temporally from a co-located wedgelet block of a previouslydecoded sample array of a sample array sequence including sample array302. Alternatively, an explicit signaling of the end point 318 of thewedgelet separation line may be used. The explicit signaling couldrepresent the offset of the end point 318 from a sample position lyingat an opposite position relative to start position 314 across a midpointof block 210. Other solutions are, of course, also feasible.

In this regard, it should be noted that the start point 314 could bedefined by decoder 500 in step 406′, to correspond to the nth sampleposition, the (n+1)th sample position or a subpixel positiontherebetween.

Many of the combination possibilities mentioned above in sections 5.1and 5.2 are also transferable to the embodiment of the present section.For example, the coding mode of decoder 500 realized by blocks 406′ and412′ may represent a subsidiary fallback functionality triggered with acommon predetermined value of a common coding option identifier with thewedgelet separation line continuation concept of section 5.1representing the default coding mode which is performed instead wheneverone of the set of candidate neighbor blocks has a wedgelet separationline continuing into the current block 210. The other generalizationsand modifications are also feasible. For example, decoder 500 could alsosupport a contour partitioning mode and so forth.

According to FIG. 20, the following information may be present in datastream for block 210: 1) the coding option identifier having therespective predetermined state triggering the steps 406′-412′, 2)optionally, refinement information such as an end position offset, 3)optionally, coding parameters-such as CPV or CPV residual—for one orboth partitions 202 a, 202 b—optional, because same may be allowed to bepredicted-spatially or temporally from neighboring samples/blocks, 4)optionally, coding parameter residual such as DeltaCPV.

FIG. 21 shows an encoder fitting to the decoder of FIG. 20. Same isindicated by reference sign 530 and is configured to perform a linederivation 434′ in accordance with step 406 and an encoding 436′ asoutlined with respect to FIG. 19 with respect to block 436.

5.4. Tile- (Pixel-) Based Bi-Segmentation of Depth/Disparity Map byThresholding a Co-Located Portion of the Picture

As became clear from the above discussion, wedgelet-based partitioningrepresents a kind of tradeoff between side information rate on the onehand and achievable variety in partitioning possibilities on the otherhand. Compared thereto, contour partitioning seems to be more complex interms of side information rate.

The idea underlying the embodiments described further below is that theability to alleviate the constraints of the partitioning to the extentthat the partitions have to be wedgelet partitions, enables applyingrelatively uncomplex statistical analysis onto overlaid spatiallysampled texture information in order to derive a good predictor for thebi-segmentation in a depth/disparity map. Thus, in accordance with thisidea, it is exactly the increase of the freedom which alleviates thesignaling overhead provided that co-located texture information in formof a picture is present, and that meaningful texture variation isvisible therein. A possible implementation of this idea, which exploitsthis idea, was described above in section 3.2.2, but is described inmore detail below in more generic terms. Again, all the detailsdescribed in section 3.2.2 and the other sections are to be understoodas possible realization details, which may be combined with thedescription presented below individually.

In particular, FIG. 22 shows a decoder 600 in accordance with such anembodiment of the present invention. The decoder 600 is forreconstructing a predetermined block of a depth/disparity map 213associated with a picture 215 from a data stream 304. The decodercomprises a segmenter 602, a spatial transferrer 604 and a decoder 606.The decoder 600 may be configured as described above with respect to anyof the decoding branches 106 _(d,) ¹/₂. That is, the decoder 600 mayoperate on a block-basis. Further, same may be implemented as a hybridvideo decoder. The subdivision of the depth/disparity map 213 intoblocks may be derived completely from the subdivision of picture 215into blocks, or may deviate therefrom, wherein the subdivision of thedepth/disparity map may be signaled within the data stream 304 or may beotherwise known to the decoder 600.

Segmenter 602 is configured to segment a reference block 216 of picture215, co-located to the predetermined block 210 of the depth/disparitymap 213, by thresholding the picture 215 within the reference block 216to obtain a bi-segmentation of the reference block into first and secondpartitions.

The spatial transferrer 604 then transfers the bi-segmentation of thereference block 216 of the picture onto the predetermined block 210 ofthe depth/disparity map 213 so as to obtain first and second partitions202 a and 202 b of the predetermined block 210.

The decoder 606 is configured to decode a predetermined block 210 inunits of the first and second partitions 202 a and 202 b. Thefunctionality of decoder 606 corresponds to the functionality describedabove with respect to boxes 310, 412 and 412′.

Thinking of FIGS. 1 to 3, the segmenter and transferrer functionalitycould be included within the exchange module 52 and 110, respectively,while the functionality of decoder 606 could be implemented in theintra-prediction module, for example.

As described above with respect to section 3.2.2 in which thedescription may represent possible implementation details for theelements of FIG. 22, individually, the segmenter 602 may be configuredto, in thresholding, individually check values of the picture 215 withinthe reference block 216 at tiles 608 of a two-dimensional subdivision ofthe reference block 216, as to whether the respective value is greaterthan or lower than a respective predetermined value, so that each of thefirst and second partitions 202 a and 202 b of the reference block 216of the picture 215 is a set of tiles 608 which together completely coverthe reference block 216 of the picture 215 and are complementary to eachother. That is, the thresholding may be performed at sample resolutionin which case the tiles 608 correspond to the individual samples 610 ofpicture 215. It should be mentioned that decoder 600 may also beresponsible for reconstructing the picture 215 in that the values whichare the subject of the individual check in thresholding are thereconstructed values of the reconstructed picture 215. In particular, asdescribed with respect to FIGS. 1 to 3, decoder 600 may be configured toreconstruct picture 215 prior to depth/disparity map 213 associatedtherewith.

As already mentioned above, the segmenter 602 may be configured to, insegmenting, apply morphological hole filling and/or low-pass filteringonto a result of the thresholding in order to obtain the bi-segmentationof the reference block 216 into the first and second partitions. Thisavoids the occurrence of too many isolated segments of the partitions ofthe bi-segmentation obtained from the reference block 216 which wouldthen be spatially transferred by spatial transferrer 604 where, however,such abrupt depth changes are significantly less probable to visiblyoccur. Naturally, the encoder would perform the same.

Further, decoder 600 and segmenter 602 could be configured to, inthresholding, determine a measure for a central tendency of thereconstructed sample values of the reference block 216 of the picture215 and perform the thresholding by comparing each reconstructed samplevalue of the reference block 216 of the picture 215 with a respectivethreshold which depends on the measure determined. As described above,the threshold may be globally defined among the samples 610 withinreference block 216. As the central tendency, some mean value may beused, such as the arithmetic mean or a median value.

As described above in section 4.2, decoder 600 could be configured tosupport the availability of the coding mode represented by blocks 602 to606 merely in case of an a-priori determined dispersion of value ofsamples within the reference block 216 of the picture 215 exceeding apredetermined threshold. If not, the bi-segmentation found by thethresholding would very likely not form a good predictor for theappearance of the block 210 of the depth/disparity map and, accordingly,this coding mode may not allowed for this block. By suppressing the modepossibility, a disadvantageous and unnecessary increase of the number ofsymbol values of the respective coding option identifier for which anentropy probability estimate would have to be taken into account, isavoided.

According to FIG. 22, the following information may be present in datastream for block 210: 1) the coding option identifier having therespective predetermined state triggering the steps 602-604, 2)optionally, information steering the bi-segmentation such as thethreshold, subsequent filtering/hole filling directivities or the like,3) optionally, coding parameters—such as CPV or CPV residual—for one orboth partitions 202 a, 202 b—optional, because same may be allowed to bepredicted—spatially or temporally from neighboring samples/blocks, 4)optionally, coding parameter residual such as DeltaCPV.

All further variations mentioned above with respect to the embodimentsof FIGS. 16, 18 and 20 are also applicable to the embodiment of FIG. 22.This is especially true for the use of the prediction result as a partof a reference in a prediction loop of the decoder 600 and thepossibility of combining the coding mode of FIG. 22 with any of theother coding modes described in any of sections 5.1 to 5.3 or withrespect to the variations described above in sections 3 to 4.

FIG. 23 shows a possible implementation of an encoder fitting to thedecoder of FIG. 22. The encoder of FIG. 23 is generally indicated withreference sign 630 and is configured to encode a predetermined block ofa depth/disparity map associated with a picture into a data stream 304.The encoder comprises a segmenter 632 and a spatial transferrer 634which operate like components 602 and 604 of FIG. 22 in that theyoperate on an internally reconstructed version of previously encodedportions of data stream 304. The encoder 636 encodes the predeterminedblock in units of the resulting partitions.

5.5. Dependency of the Availability of the Bi-Segmentation Transfer fromPicture to Depth/Disparity Map on the Sample Value Dispersion within theReference Block of the Picture

The idea underlying the embodiment outlined below was already mentionedabove in section 4.2, namely the idea according to which the derivationof a bi-segmentation based on a co-located reference block within apicture with subsequent transferal of the bi-segmentation onto thecurrent block of the depth/disparity map is merely reasonable if thelikelihood of achieving a good approximation of the content of thecurrent block of the depth/disparity map is sufficiently high so as tojustify the reservation of a respective predetermined value of acorresponding coding option identifier in order to trigger thisbi-segmentation transferal mode. In other words, side information ratemay be saved by avoiding the necessity to take the respectivepredetermined value of the coding option identifier for the currentblock of the depth/disparity map into account when entropy-coding thiscoding option identifier in case the respective bi-segmentationtransferal is very likely not to be selected anyway.

Thus, in accordance with a modified embodiment of the decoder 600 ofFIG. 22, decoder is generally constructed similar to the decoder of FIG.20, so that reference is made to the above description as far aspossible implementations of the decoder 600 in general are concerned.However, the segmenter 602 is not restricted to be configured to segmentthe reference block 216 into a contour partition, nor into a wedgeletpartition. Rather segmenter 602 is merely configured to segment thereference block 216 of the picture 215 depending on a texture feature ofthe picture 215 within the reference block 216 so as to obtain abi-segmentation of the reference block into first and second partitions.For example, segmenter 602 may, in accordance with such a modifiedembodiment, use edge detection in order to detect a possible extensiondirection of a wedgelet separation line in order to transfer the thuslocated line from block 216 spatially onto depth/disparity block 210 byspatial transferrer 604. Other possible bi-segmentations by segmenter602 would also be feasible.

Beyond that, however, the decoder 600 would, in accordance with thisembodiment, be configured such that the segmentation by segmenter 602,the spatial transfer by spatial transferrer 604 and the decoding wouldform one of a first set of coding options of the decoder 600, which isnot part of a second set of coding options of the decoder 600, whereinthe decoder would further be configured to determine a dispersion ofvalues of samples within the reference block 216 of the picture 215, toretrieve a coding option identifier from the data stream 304 and to usethe coding option identifier as an index into the first set of codingoptions in case of the dispersion exceeding a predetermined threshold,with performing the segmentation, spatial transfer and decoding in boxes602 to 606 onto the predetermined block 210 if the index points to theone coding option, and as an index into the second set of coding optionsin case of the dispersion succeeding the predetermined threshold. Thus,signaling overhead for signaling the coding option identifier may besaved. As the dispersion, the mean absolute difference, the standarddeviation, or the variance may be used.

With regard to further modifications of the embodiment of thejust-mentioned modification of FIG. 22, reference is made to section 5.4and the description with respect to section 4.2.

A corresponding encoder may be derived from the encoder of FIG. 23.

5.6. Effective Prediction by Bi-Partitioning Using Prediction of One orBoth Constant Partition Values from Neighboring Samples

As already outlined above with respect to the various embodimentsdescribed so far, the way of predicting a current block by assigningconstant partition values to the partitions of a bi-partitioning of ablock is quite effective, especially in case of a coding sample arrayssuch as depth/disparity maps where the content of these sample arrays ismostly composed of plateaus or simple connected regions of similar valueseparated from each other by steep edges. Nevertheless, even thetransmission of such constant partition values needs a considerableamount of side information which should be avoided.

The idea underlying the embodiments described further below is that thisside information rate may be reduced if mean values of values ofneighboring samples associated or adjoining the respective partitionsare used as predictors for the constant partition values. The inventorsfound out that such a coding mode for blocks of the sample array mayeven leave a signaling of a refinement of the respective constantpartition value away.

FIG. 24 shows a decoder 700 which is for reconstructing a sample array302 from a data stream 304. The decoder 700 may be configured toreconstruct the sample array 302 using a block-based decoding and may beconfigured to use hybrid decoding. Generally, all the possibleimplementations described above in sections 5.1 to 5.5 also apply to thedecoder 700 of FIG. 24. Naturally, all the possible implementations forpartitioning a current block 210 into two partitions merely representoptional alternatives for the decoder of FIG. 700 which may, in thisregard, also be implemented differently.

In particular, the decoder 700 is configured to perform different tasksor functions to derive the prediction of a current block 210. Inparticular, decoder 700 is configured to perform a derivation 702 of abi-partition of a predetermined block 210 of the sample array 302 into afirst partition illustrated by hatched samples, and a second partitionillustrated by non-hatched samples. Further, decoder 700 is configuredto perform an association 704 of each of neighboring samples of thesample array 302, adjoining to the predetermined block 210, with arespective one of the first and second partitions so that eachneighboring sample adjoins the partition with which same is associated.In FIG. 24 the neighboring samples, which are the subject of theassociation 704, are illustrated by two different kinds of hatching,namely dotted hatching and cross hatching. The dot-hatched ones showsamples adjoining samples of block 210, which belong to one partition ofblock 210, whereas the cross-hatched ones adjoin samples of block 210which belong to the other partition. As described above with respect tosections 5.1 to 5.4, decoder 700 may use an appropriate coding/decodingorder among blocks 303 of sample array 302 in order to achieve a highprobability for availability of neighboring samples of blocks 303 of thesample array 302 which have already been reconstructed by decoder 700.

Of course, it may occur that the available neighboring samples, i.e. theneighboring samples of block 210 positioned within already reconstructedblocks 303 of the sample array 302, merely join to one of the partitionsof block 210. In that case, the data stream 304 may explicitly transmita constant partition value for the respective other partition to whichnone of the neighboring samples adjoin. Alternatively, some otherfallback procedure may be performed by decoder 700 in that case. Forexample, decoder 700 may, in that case, set this missing constantpartition value to a predetermined value or a value determined from along-term mean among previously reconstructed values of sample array 302and/or some other previously reconstructed sample array.

Finally, in a prediction 706, decoder 700 predicts the predeterminedblock 210 by assigning a mean value of values of the neighboring samplesassociated with the first partition to samples of the sample arraypositioned within the first partition and/or a mean value of values ofthe neighboring samples associated with a second partition to samples ofthe sample array positioned within the second partition.

The decoder 700 may be configured to refine the prediction of thepredetermined block 210 using refinement information within the datastream, namely by applying a first refinement value within therefinement information onto the mean value of values of the neighboringsamples associated with the first partition, and/or applying a secondrefinement value within the refinement information onto the mean valueof values of the neighboring samples associated with the secondpartition. In this regard, the decoder 700 may further be configured to,in applying the first and/or second refinement value, linearlycombine—such as add—the first and/or second refinement value with themean value of values of the neighboring samples associated with thefirst partition, and/or the mean value of values of the neighboringsamples associated with the second partition, respectively. The decoder700 may be configured to, in applying the first and/or second refinementvalue, retrieve the first and/or second refinement value from the datastream and scale the first and/or second refinement value as retrievedusing a quantization step size depending on a reference quantizationstep size at which a predetermined spatially sampled component-textureand/or depth/map—associated with the sample array is transmitted withinthe data stream. The sample array may, for example, be a depth map, butthe reference quantization step size may be used by decoder 700 toreconstruct a texture sample array from the bitstream, with which thedepth map is associated. Further reference is made to the respectiveportions in sections 3.3.2 for further details.

The decoder is configured to, in deriving the bi-partition of apredetermined block of the sample array into first and secondpartitions, predict a position of a wedgelet separation line within thepredetermined block of the sample array depending on a wedgeletseparation line of a neighboring block of the predetermined block suchthat the wedgelet separation line at the predicted position forms anextension of the wedgelet separation line of the neighboring block intothe predetermined block. The decoder is further configured to refine thepredicted position of the wedgelet separation line using refinementinformation within the data stream, the wedgelet separation line of thepredetermined bock dividing the predetermined block into the first andsecond partitions.

As described, the decoder 700 may do the bi-segmentation using any ofthe ideas set out in sections 5.1 to 5.5. Decoder 700 may be configuredto predict a reference block of the sample array 302, neighboring thepredetermined block 210, using intra-prediction by filling the referenceblock by copying reconstructed values of samples of the sample array,neighboring the first block, along an intra-prediction direction intothe reference block. In deriving the bi-partition of a predeterminedblock of the sample array into first and second partitions, decoder 700may predict a position of a wedgelet separation line within thepredetermined block 210 by setting an extension direction of thewedgelet separation line within the predetermined block depending on theintra-prediction direction, the wedgelet separation line dividing thepredetermined block into the first and second partitions.

Alternatively, the decoder 700 may, if the sample array 302 is adepth/disparity map associated with a picture, be configured to segmenta reference block of the picture, co-located to the predetermined block210, by thresholding the picture within the reference block to obtain abi-segmentation of the reference block into first and predeterminedpartitions, and to spatially transfer the bi-segmentation of thereference block of the picture onto the predetermined block of thedepth/disparity map so as to obtain the first and second partitions.

The decoder may further be further configured to use the predeterminedblock as a reference in a prediction loop of the decoder.

FIG. 25 shows a possible embodiment for an encoder 730 fitting to thedecoder 700 of FIG. 24. The encoder 730 for encoding a sample array intoa data stream is configured to derive 732 a bi-partition of apredetermined block of the sample array into first and secondpartitions, and to associate 734 each of neighboring samples of thesample array, adjoining to the predetermined block, with a respectiveone of the first and second partitions so that each neighboring sampleadjoins the partition with which same is associated. The encoder isfurther configured to predict 736 the predetermined block by assigning amean value of values of the neighboring samples associated with thefirst partition to samples of the sample array positioned within thefirst partition and a mean value of values of the neighboring samplesassociated with the second partition to samples of the sample arraypositioned within the second partition.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus. Some or all of the method steps may be executed by (or using)a hardware apparatus, like for example, a microprocessor, a programmablecomputer or an electronic circuit. In some embodiments, some one or moreof the most important method steps may be executed by such an apparatus.

Depending on certain implementation requirements, embodiments of theinvention can be implemented in hardware or in software. Theimplementation can be performed using a digital storage medium, forexample a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM,an EEPROM or a FLASH memory, having electronically readable controlsignals stored thereon, which cooperate (or are capable of cooperating)with a programmable computer system such that the respective method isperformed. Therefore, the digital storage medium may be computerreadable.

Some embodiments according to the invention comprise a data carrierhaving electronically readable control signals, which are capable ofcooperating with a programmable computer system, such that one of themethods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedon a machine readable carrier.

Other embodiments comprise the computer program for performing one ofthe methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein. The data carrier, the digital storagemedium or the recorded medium are typically tangible and/ornon-transitionary.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

A further embodiment according to the invention comprises an apparatusor a system configured to transfer (for example, electronically oroptically) a computer program for performing one of the methodsdescribed herein to a receiver. The receiver may, for example, be acomputer, a mobile device, a memory device or the like. The apparatus orsystem may, for example, comprise a file server for transferring thecomputer program to the receiver.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods may be performed by any hardware apparatus.

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which will beapparent to others skilled in the art and which fall within the scope ofthis invention. It should also be noted that there are many alternativeways of implementing the methods and compositions of the presentinvention. It is therefore intended that the following appended claimsbe interpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

What is claimed:
 1. A decoder for reconstructing a block of a depth mapassociated with a texture picture from a data stream, configured to:determine a texture threshold based on a statistic of sample values of areference block of the texture picture; determine a contour partition ofthe reference block of the texture picture by comparing each sample ofthe reference block with the texture threshold; predict a contourpartition of the block of the depth map based on the contour partitionof the reference block such that the block of the depth map is segmentedinto two portions; and decode the block of the depth map based on thecontour partition of the block of the depth map.
 2. The decoderaccording to claim 1, configured to, in determining the contourpartition of the reference block, individually check values of thetexture picture within the reference block at tiles of a two-dimensionalsubdivision of the reference block, as to whether the respective valueis greater than or lower than a respective predetermined value, so thateach of first and second portions of the reference block of the texturepicture is a set of the tiles which together completely cover thereference block of the texture picture and are complementary to eachother.
 3. The decoder according to claim 2, configured to, indetermining the contour partition of the reference block, individuallycheck values of the texture picture within the reference block at sampleresolution so that each tile corresponds to a sample position of thereference block.
 4. The decoder according to claim 1, configured to, indetermining a contour partition of the reference block, applymorphological hole filling and/or low-pass filtering onto a result ofthe comparing in order to acquire two portions of the reference block.5. The decoder according to claim 1, configured to, in determining thetexture threshold, determine a measure for a central tendency ofreconstructed sample values of the reference block of the texturepicture, wherein the measure represents the texture threshold.
 6. Thedecoder according to claim 1, further configured to determine adispersion of value of samples within the reference block of the texturepicture; receive a coding option identifier from the data stream; anduse the coding option identifier as an index to perform the determiningof the texture threshold, the determining of the contour partition ofthe reference block, the predicting of the contour partition of theblock of the depth map, and the decoding operations in case of thedispersion exceeding a predetermined threshold.
 7. The decoder accordingto claim 1, wherein the statistic is a mean of the sample values of thereference block.
 8. An encoder for encoding a block of a depth mapassociated with a texture picture into a data stream, configured to:determine a texture threshold based on a statistic of sample values of areference block of the texture picture; determine a contour partition ofthe reference block of the texture picture by comparing each sample ofthe reference block with the texture threshold; predict a contourpartition of the block of the depth map based on the contour partitionof the reference block such that the block of the depth map is segmentedinto two portions; and encode, into the data stream, the block of thedepth map based on the contour partition of the block of the depth map.9. The encoder according to claim 8, configured to, in determining thecontour partition of the reference block, individually check values ofthe texture picture within the reference block at tiles of atwo-dimensional subdivision of the reference block, as to whether therespective value is greater than or lower than a respectivepredetermined value, so that each of first and second portions of thereference block of the texture picture is a set of the tiles whichtogether completely cover the reference block of the texture picture andare complementary to each other.
 10. The encoder according to claim 9,configured to, in determining the contour partition of the referenceblock, individually check values of the texture picture within thereference block at sample resolution so that each tile corresponds to asample position of the reference block.
 11. The encoder according toclaim 8, configured to, in determining the contour partition of thereference block, apply morphological hole filling and/or low-passfiltering onto a result of the comparing in order to acquire twoportions of the reference block.
 12. The encoder according to claim 8,configured to, in determining the texture threshold, determine a measurefor a central tendency of reconstructed sample values of the referenceblock of the texture picture, wherein the measure represents the texturethreshold.
 13. The encoder according to claim 8, further configured to:determine a dispersion of value of samples within the reference block ofthe texture picture; and encode a coding option identifier into the datastream, wherein the coding option identifier is used as an index toperform the operations forming the determining of the texture threshold,the determining of the contour partition of the reference block, thepredicting of the contour partition of the block of the depth map, andthe decoding operations in case of the dispersion exceeding apredetermined threshold.
 14. The encoder according to claim 8, whereinthe statistic is a mean of the sample values of the reference block. 15.A non-transitory computer-readable medium for storing data associatedwith a video, comprising: a data stream stored in the non-transitorycomputer-readable medium, the data stream comprising encoded informationof a reference block of a texture picture of the video and encodedinformation of a block of a depth map, which corresponds to the texturepicture, of the video, wherein the block of the depth map is decodedusing a plurality of operations including: determining a texturethreshold based on a statistic of sample values of a reference block ofthe texture picture; determining a contour partition of the referenceblock of the texture picture by comparing each sample of the referenceblock with the texture threshold; predicting a contour partition of theblock of the depth map based on the contour partition of the referenceblock such that the block of the depth map is segmented into twoportions; and decoding the block of the depth map based on the contourpartition of the block of the depth map.
 16. The computer-readablemedium according to claim 15, wherein determining a contour partition ofthe reference block includes individually checking values of the texturepicture within the reference block at tiles of a two-dimensionalsubdivision of the reference block, as to whether the respective valueis greater than or lower than a respective predetermined value, so thateach of first and second portions of the reference block of the texturepicture is a set of the tiles which together completely cover thereference block of the texture picture and are complementary to eachother.
 17. The computer-readable medium according to claim 16, whereindetermining a contour partition of the reference block includesindividually checking values of the texture picture within the referenceblock at sample resolution so that each tile corresponds to a sampleposition of the reference block.
 18. The computer-readable mediumaccording to claim 15, wherein determining a contour partition of thereference block includes applying morphological hole filling and/orlow-pass filtering onto a result of the comparing in order to acquiretwo portions of the reference block.
 19. The computer-readable mediumaccording to claim 13, wherein determining the texture thresholdincludes determining a measure for a central tendency of reconstructedsample values of the reference block of the texture picture, wherein themeasure represents the texture threshold.
 20. The computer-readablemedium according to claim 15, wherein the statistic is a mean of thesample values of the reference block.